New Trends to Treat Muscular Atrophy: A Systematic Review of Epicatechin

Epicatechin is a polyphenol compound that promotes skeletal muscle differentiation and counteracts the pathways that participate in the degradation of proteins. Several studies present contradictory results of treatment protocols and therapeutic effects. Therefore, the objective of this systematic review was to investigate the current literature showing the molecular mechanism and clinical protocol of epicatechin in muscle atrophy in humans, animals, and myoblast cell-line. The search was conducted in Embase, PubMed/MEDLINE, Cochrane Library, and Web of Science. The qualitative analysis demonstrated that there is a commonness of epicatechin inhibitory action in myostatin expression and atrogenes MAFbx, FOXO, and MuRF1. Epicatechin showed positive effects on follistatin and on the stimulation of factors related to the myogenic actions (MyoD, Myf5, and myogenin). Furthermore, the literature also showed that epicatechin can interfere with mitochondrias’ biosynthesis in muscle fibers, stimulation of the signaling pathways of AKT/mTOR protein production, and amelioration of skeletal musculature performance, particularly when combined with physical exercise. Epicatechin can, for these reasons, exhibit clinical applicability due to the beneficial results under conditions that negatively affect the skeletal musculature. However, there is no protocol standardization or enough clinical evidence to draw more specific conclusions on its therapeutic implementation.


Introduction
There has been a growing interest in the study of catechins and the properties reported in the scientific literature related to their antioxidant, regenerative, and anti-inflammatory capacity [1][2][3].
There are four major subclasses of catechins: Epicatechin (EC), Epigallocatechin (EGC), Epicatechin gallate (ECG), and Epigallocatechin gallate (EGCG) [2].Among the different catechins, EC and EGCG have greater effects on the skeletal musculature.Catechins exhibit beneficial effects on skeletal muscle, specifically on myoblast differentiation, but only epicatechin promotes mitochondrial biogenesis and angiogenesis, as described by Li et al. [4].
EC is a polyphenolic compound found at high concentrations in certain fruits and vegetables, including tea leaves, black grapes, chocolate, apples, raspberries, and cherries [2,5,6].EC is mainly extracted from green tea (Camellia sinensis) [4,5].The consumption of such polyphenols has been linked to several positive effects on diseases involving oxidative stress, such as cancer, diabetes, cardiovascular, and degenerative diseases [7,8].Figure 1 shows the biological properties of epicatechin.
Nutrients 2024, 16, x FOR PEER REVIEW 2 of 2 different catechins, EC and EGCG have greater effects on the skeletal musculature Catechins exhibit beneficial effects on skeletal muscle, specifically on myoblas differentiation, but only epicatechin promotes mitochondrial biogenesis and angiogenesis, as described by Li et al. [4].EC is a polyphenolic compound found at high concentrations in certain fruits and vegetables, including tea leaves, black grapes, chocolate, apples, raspberries, and cherrie [2,5,6].EC is mainly extracted from green tea (Camellia sinensis) [4,5].The consumption o such polyphenols has been linked to several positive effects on diseases involvin oxidative stress, such as cancer, diabetes, cardiovascular, and degenerative diseases [7,8 Figure 1 shows the biological properties of epicatechin.More recently, EC has shown the potential capacity to mitigate and delay the loss o muscle mass in diseases that affect the musculoskeletal system [4,[9][10][11].
The role of dietary supplements in activating specific pathways that mitigate o neutralize muscle atrophy in patients with diseases that participate in the same muscl atrophy signal pathway has been highlighted [12].For example, sarcopenia is a skeleta disorder that negatively affects muscle mass and is closely related to cardiovascula disease and other chronic diseases [13].
Muscular atrophy is a musculoskeletal disease characterized by the loss of cell size In this process, there is a decrease in proteins and organelles and an increase in th expression of genes associated with muscle atrophy, accelerating protein catabolism and compromising function and performance [4].In addition, muscle atrophy occurs i response to different conditions such as diabetes, cardiac failure, cancer, fasting, agin [14,15], obesity, rheumatoid arthritis, and physical inactivity [13].
The regulation of skeletal muscle growth occurs via the IGF-PI3K-AKT pathway.Th enzyme phosphatidylinositol-3-kinase (PI3K) allows glycogen to enter cells by facilitated diffusion; subsequently, the pyruvate dehydrogenase kinase (PDK1) transmits the PI3K signal, acting as a second messenger.Then, AKT (Protein kinase B) acts on protei signaling pathways, activating the largest signal integrative pathway, mTOR, which More recently, EC has shown the potential capacity to mitigate and delay the loss of muscle mass in diseases that affect the musculoskeletal system [4,[9][10][11].
The role of dietary supplements in activating specific pathways that mitigate or neutralize muscle atrophy in patients with diseases that participate in the same muscle atrophy signal pathway has been highlighted [12].For example, sarcopenia is a skeletal disorder that negatively affects muscle mass and is closely related to cardiovascular disease and other chronic diseases [13].
Muscular atrophy is a musculoskeletal disease characterized by the loss of cell size.In this process, there is a decrease in proteins and organelles and an increase in the expression of genes associated with muscle atrophy, accelerating protein catabolism and compromising function and performance [4].In addition, muscle atrophy occurs in response to different conditions such as diabetes, cardiac failure, cancer, fasting, aging [14,15], obesity, rheumatoid arthritis, and physical inactivity [13].
The regulation of skeletal muscle growth occurs via the IGF-PI3K-AKT pathway.The enzyme phosphatidylinositol-3-kinase (PI3K) allows glycogen to enter cells by facilitated diffusion; subsequently, the pyruvate dehydrogenase kinase (PDK1) transmits the PI3K signal, acting as a second messenger.Then, AKT (Protein kinase B) acts on protein signaling pathways, activating the largest signal integrative pathway, mTOR, which, through the substrate S6K1 and the binding protein 4EBP1, regulates protein quality, promoting muscle growth [4].
In this muscle restructuring, several myogenic regulation factors participate, mainly in the proliferation stages.Myoblast determination protein (MyoD) and Myogenic factor 5 (Myf5) are involved, which are necessary for the determination of the myobrast; later, in the differentiation phase, myogenin and Miogenic regulatory factor 4 (MRF4) are expressed [9].
As described by Savary-Auzeloux et al. (2013) [23], nutritional supplementation of antioxidants/polyphenols contributes to the signaling of different factors involved in protein synthesis, even in absence of physical exercise and/or skeletal muscle recovery from disuse.
Furthermore, dietary supplements activate and modulate depending on their specific composition and standard mechanism of action.Some common biochemical pathways involved include: • mTOR signaling: many dietary supplements target the mammalian rapamycin (mTOR) signaling pathway, related to protein turnover and autophagy (a process of recycling resulting in degradation of the body's own tissue) [24]; • AMP-activated protein kinase (AMPK) pathway: AMPK is a metabolic pathway that regulates energy metabolism and cellular energy homeostasis.Some supplements can activate the AMPK pathway to promote processes using fat as an energy source [25]; • nuclear transcription factor kappa B (NF-kB) pathway: NF-kB is a pathway in inflammatory and immune response.Supplements can modulate the NF-kB pathway to regulate inflammation and promote a healthy immune response [26]; • peroxisome proliferator-activated receptors (PPAR) pathway: PPARs are a family of receptors that regulate metabolism of lipids and energy homeostasis.Oral nutrition supplements can activate PPARs to modulate metabolism and the inflammatory response [27].
Clinical studies have related the catechins to the protective effects of the skeletal musculature by inducing myogenic differentiation and improving muscle structure and function [28,29].
In the skeletal muscle, EC acts directly and indirectly in the protein synthesis signaling [30], reduces the catabolic effect [31,32] by stimulating the PI3K/Akt pathway and by inactivating the autophagic genes FoxO, MAFbx, and MuRF [2].This mechanism of action of EC in the muscle occurs by inhibiting the degradation proteins and increasing mitochondrial biogenesis [6,33].
Research in animals that received catechins presented an increase in the Muscle Regulatory Factors (MRF), including MyoD, Myf5, and Myogenin, and a decrease occurred in myostatin, a protein identified as modulatory of the primary catabolic pathways, participating in the signaling that regulates the muscular atrophy [9,34].
Due to the great benefits of EC supplementation and its clinical relevance in the treatment of diseases that affect the skeletal muscles, it is crucial to summarize the evidence available on the effects of this polyphenol using the search strategy.Despite the positive effects of EC, there are conflicting results and non-standardized therapeutic protocols.
Our systematic review identifies substantive gaps in the current understanding of the effects of epicatechin on muscle atrophy, providing a solid foundation to drive future investigations.By highlighting inconsistencies and deficiencies in the existing literature, our approach not only consolidates existing knowledge but also catalyzes the pressing need for subsequent research to fill these gaps and enhance our understanding of the clinical applicability of EC in skeletal muscular atrophy.
In this context, this systematic review aimed to analyze the existing literature, addressing epicatechin supplementation's molecular effects and clinical protocol to counteract muscle atrophy in humans, animals, and myoblast cell lines.

Data Extraction Methods
This systematic review was substantiated through the PICO strategy [35]-P: use of EC in humans and animals; I: application of EC in muscular atrophy; C: comparison with the control/placebo group; O: effects on the skeletal musculature.The choice of the PubMed/MEDLINE, Web of Science, Embase, and Cochrane Library databases were based on the PICO strategy in order to evaluate the clinical protocols and protein turnover effects of EC supplementation on skeletal musculature atrophy condition.
All databases were searched in August-September 2023, including the terms registered in the Medical Subject Headings (MeSH): Catechin, muscular atrophy, muscle regeneration, epicatechin, muscle, and damage by associating the following keywords with no restrictions concerning the year of publication of the articles: "Catechin and muscular atrophy", "Epicatechin and muscle regeneration", "Epicatechin and muscle and damage".
Two authors conducted the search to achieve a more reliable selection of articles in the databases.
Two independent authors carried out the selection of articles and the evaluation of the full text.No filters were used in the databases in order to avoid losing relevant studies.In addition, studies from gray literature were analyzed to identify potentially relevant studies for this systematic review.Furthermore, experts in the field were contacted to obtain pertinent information or recommendations for important articles.
The articles were selected considering the eligibility criteria and PRISMA checklist [36].

Inclusion Criteria
• In vivo and in vitro studies that evaluated EC in the treatment of muscular atrophy.

•
Studies with specifications of the dosage of EC used, treatment time, and administration route.• Systematic literature reviews.

Exclusion Criteria
• Articles that used another type of catechin or flavonoid.

•
Studies that did not analyze EC effects on skeletal musculature.
To search, the keywords were combined in each database.The articles were selected by title and then by reading the abstracts; thus, they were organized, and subsequently, the articles were restricted according to the eligibility criteria, following the proposed methodology and the PRISMA checklist [36].Figure 2 shows the search design strategy in the databases.

Data Synthesis Methods-Search Results
A total of 253 articles were identified in search for this systematic review.In PUBMED/MEDLINE database, 111 articles were verified, 30 studies in Web of Science, 105 in Embase, and 7 articles in Cochrane Library.After removing the duplicated articles, 230 remained, of which 145 studies were eliminated as they were unrelated to the subject of investigation.Of the 85 articles remained, 1 record could not be located, and no response was received when the authors were contacted.As such, 84 reports were assessed for eligibility and, after reading, 66 articles were excluded: 47 used another type of polyphenol, 12 studies used EC in other muscle tissue, and 7 abstracts were from congresses.Thus, 18 articles were included (11 studies in animals, 6 in humans, and 1 in vitro research).
In addition, 328 reports were located on websites and citation trackers.After removing duplicate records, 255 articles were screened; 178 were excluded and the remaining 77 reports were advanced to reading the full text.Of these, 70 articles were excluded.As such,, only seven reports matched the eligibility criteria.
Finally, 25 articles were included in this systematic study (15 studies in animals, 7 in humans, and 3 in vitro articles).Tables 1-3 show the main information about the 25 studies selected in humans, animals, and in vitro, respectively.

Data Synthesis Methods-Search Results
A total of 253 articles were identified in search for this systematic review.In PUBMED/ MEDLINE database, 111 articles were verified, 30 studies in Web of Science, 105 in Embase, and 7 articles in Cochrane Library.After removing the duplicated articles, 230 remained, of which 145 studies were eliminated as they were unrelated to the subject of investigation.Of the 85 articles remained, 1 record could not be located, and no response was received when the authors were contacted.As such, 84 reports were assessed for eligibility and, after reading, 66 articles were excluded: 47 used another type of polyphenol, 12 studies used EC in other muscle tissue, and 7 abstracts were from congresses.Thus, 18 articles were included (11 studies in animals, 6 in humans, and 1 in vitro research).
In addition, 328 reports were located on websites and citation trackers.After removing duplicate records, 255 articles were screened; 178 were excluded and the remaining 77 reports were advanced to reading the full text.Of these, 70 articles were excluded.As such, only seven reports matched the eligibility criteria.
Finally, 25 articles were included in this systematic study (15 studies in animals, 7 in humans, and 3 in vitro articles).Tables 1-3 show the main information about the 25 studies selected in humans, animals, and in vitro, respectively.

Oral route
The EIMD protocol consisted in the hip fastening to the dynamometer at 85 • of bending using straps to isolate the knee (5 series of 10 maximum concentric and eccentric contractions of the knee.
No significant modifications were observed between the groups for all the measures in the bending exercises.The participants received two capsules in the morning and two in the evening.The brachial biceps muscle biopsies were collected preand post-treatment.
Follistatin significantly increased, while myostatin decreased.There was a significant increment of tissue markers Myf5, MyoD, myogenin, and MEF2a.EC stimulated PGC1α (a coactivator of mitochondrial biogenesis).p < 0.05  In the DT-14-W and DT-14-Epi (groups 2 and 3), the VEGF-A protein was higher compared to groups 1 and 2. Complex I expression was increased in the DT-14-Epi group compared to the group 1.However, the expression of complex III protein was significantly greater in the group 4. The fiber area was greater in the trained and group 4. p ≤ 0.05 The muscle strength was evaluated by hand grip dynamometry (three times with each hand, alternating the hand and resting for 10 s to prevent fatigue).

Gavage
For the hind limb suspension protocol, the animals were placed in a cage with a steel bar.The soleus, medial, and gastrocnemius muscles were removed from both hind limbs.HS-EC showed significantly higher FCSA.In HS-Epi there was a slight decrease in FP compared to the control group.VEGF-A was lower in the vehicle or epicatechin groups.HS-Epi showed a significant increase in mTOR, Akt, and TFAM.PGC-1β was only induced in HS-Epi, and CcO was similar to the control.FoxO and GSK-3β were induced in HS-V.

Discussion
Coadjuvant approaches in musculoskeletal diseases have provided beneficial results to the quality of life of the affected individuals [62][63][64].
The main pathways associated with muscle atrophy involve IGF1-Akt-FoxO signaling.This pathway also participates in ROS overproduction and calcium metabolism [65].Additionally, IGF is present in different tissues of the human body [66].IGF is essential in the regenerative capacity and muscle growth by AKT phosphorylation that controls mTOR pathway [66].During the process that controls the size of the muscle fiber, genes that participate in muscle atrophy are activated, led by the main transcription factor, FoxO, and there is an increase in autophagic genes atrogin-1 (MAFbx) and MuRF1, therefore promoting protein degradation [66][67][68][69].
In addition, two proteolytic systems involved in the pathophysiology of muscle atrophy and regulate protein turnover and muscle homeostasis have been described: the ubiquitin proteasome system (UPS) and the autophagy system [69].The main genes of the UPS system are MuRF1 and MAFbx (atrogin-1) [69].An impairment of these systems can lead to an excessive activity of protein degradation and consequently compromise the contraction of myofibers [66].
In proteolytic activity, the calpain system participates in protein turnover during physical activities or disused muscles, regulating Ca 2+ signaling and contributing to the USP system by assisting the degradation of sarcomeres' proteins [65].
Seven articles in this review verified an increase in the follistatin/myostatin ratio [37,39,42,43,48,54,57].Taub et al. [37] and Mafi et al. [39] noted an increment in the follistatin levels but no significant differences in myostatin.Besides, Schwarz et al. [38] did not observe any changes in myostatin expression and no benefits in the adaptations of anaerobic exercise.In addition, myostatin inexpression may be caused by the EC stimulus on the high plasma levels of testosterone in the skeletal muscle, causing myostatin suppression [74,75].Figure 3 shows the general effects of epicatechin on protein synthesis and degradation.
As described by Li et al. [4] and Gutierrez-Salmean et al. [48], EC binds to the myostatin receptor, the C-terminus, interfering the expression and activity of myostatin.
Moreover, mitochondrial biogenesis is regulated by the expression of transcriptional coactivators, such as those from the PGC-1 family, in addition to the activity of AMPK, p38 MAPK, and TFAM signaling [4,25].
In this review, Lee et al. [49] and Gonzalez-Ruiz et al. [53] reported the effect of EC on the ubiquitin-proteasome system (UPS) through inactivation of the autophagic genes FoxO, MAFbx, and MuRF1, resulting in the blockage of the catabolic pathways in the skeletal muscle.However, some studies did not note significant effects on the reduction of protein MAFbx [54,55], the increase of follistatin, Pax7, and the decrease of atrophy markers myostatin [41], MURF and Fbox40 [55].As described by Li et al. [4] and Gutierrez-Salmean et al. [48], EC binds to the myostatin receptor, the C-terminus, interfering the expression and activity of myostatin.
Moreover, mitochondrial biogenesis is regulated by the expression of transcriptional coactivators, such as those from the PGC-1 family, in addition to the activity of AMPK, p38 MAPK, and TFAM signaling [4,25].
In this review, Lee et al. [49] and Gonzalez-Ruiz et al. [53] reported the effect of EC on the ubiquitin-proteasome system (UPS) through inactivation of the autophagic genes FoxO, MAFbx, and MuRF1, resulting in the blockage of the catabolic pathways in the skeletal muscle.However, some studies did not note significant effects on the reduction of protein MAFbx [54,55], the increase of follistatin, Pax7, and the decrease of atrophy markers myostatin [41], MURF and Fbox40 [55].
According to the existing studies, EC showed an action on the mitochondrial biogenesis of the skeletal muscle [4,6,28,76].Such a mitochondrial induction mechanism, stimulated by EC, has been proposed by Moreno-Ulloa et al. [59] and seems to be caused by epicatechin bonding to receptor GPER (G protein-coupled estrogen receptor 1), expressed in several tissues of the human body, including in the metabolic homeostasis of the skeletal muscle [77].
According to the existing studies, EC showed an action on the mitochondrial biogenesis of the skeletal muscle [4,6,28,76].Such a mitochondrial induction mechanism, stimulated by EC, has been proposed by Moreno-Ulloa et al. [59] and seems to be caused by epicatechin bonding to receptor GPER (G protein-coupled estrogen receptor 1), expressed in several tissues of the human body, including in the metabolic homeostasis of the skeletal muscle [77].
Another factor involved in skeletal muscle metabolism is the density of the blood vessels, which has the function of supplying oxygen and metabolites through the capillaries [78].Among the articles analyzed in this review, Hüttemann et al. [45], Ramirez-Sanchez et al. [46], Hüttemann et al. [47], and Lee et al. [49] noted a significantly higher increase of the capillaries compared to the control group, potentialized by physical exercise [49] even when EC was interrupted for 15 days [47].However, Lee et al. [51] verified a significant decrease of angiogenic stimulator VEGF in the epicatechin group, followed by a slight reduction, although not significant, in the perimeter of the fiber compared with the control; however, the antiangiogenic factor TPS-1 did not increase in the EC group.
In the studies in humans that evaluated muscle function, positive effects were evidenced on the walk performance at a dosage of 75 mg of EC over six months [41] and on the increase of muscle strength at a dosage of 25 mg of EC for one week [48].Mafi et al. [39] also obtained statistically significant results when epicatechin supplementation was combined with physical training.However, Schwarz et al. [38] observed aerobic adaptations with 400 mg/day of epicatechin supplementation but did not affect anaerobic training adaptations.
In humans, the acute ingestion of EC at 830 mg and 1245 mg dosages did not show any benefit to muscle recovery 24, 48, and 72 h after the exercise session [40].Several studies have noted that the acute administration of cocoa polyphenols does not improve performance or post-exercise recovery [78][79][80][81].
The research in animals showed a difference in epicatechin dosages and administration time.In the functional analysis, walking performance was enhanced at the dosage of 1 mg/kg of EC for 8 weeks [49] and in physical activity using a dose of 0.25% for 37 weeks [52].However, Ramirez-Sanchez et al. [55] observed a partial recovery of muscle strength when 1 mg/kg/day of EC was used for 30 days.In addition, Si et al. [44] obtained higher levels of AMPkα phosphorylation, suggesting that 0.25% of EC every other day for 15 weeks improves skeletal muscle function.Si et al. [52] also observed that epicatechin was able to delay muscle degeneration and improve physical activity at the dosage of 0.25% for 37 weeks.Additionally, Hüttemann et al. [45] observed an activation of AMPkα2 and an increase of fiber area in epicatechin groups.
Munguia et al. [54] used a higher dosage (2 mg of EC/kg) and obtained better results than the control in the functional test conducted in mice.Epicatechin has shown the capacity to increase the resistance to fatigue [33].
The literature has reported that higher dosages of EC in animals (4 mg kg/day for 24 days) inhibit the skeletal muscle adaptations at rest or during exercise as a result of blood flow impairment [82].Nevertheless, Mi et al. [57] used a dose at 500 and 1000 mg/kg of EC in juvenile yellow river carp and noted a great enhancement of myogenic differentiation markers.
Oral dosages of 1-2 mg/kg of epicatechin do not cause adverse effects in animals [83].However, dosages that represent more than 5% of the daily diet and are consumed for more than 3 months can produce acute cytotoxicity in liver cells, oxidative damage to pancreas DNA [84][85][86], and an enlargement of the thyroid [84].
It is crucial to consider the risk of bias in each study included in this systematic review.First, smaller samples enhance the possibility of assuming a false premise as true.Reduced sample size was observed in Taub et al. [37], McDonald et al. [42], and Qureshi et al. [43].A reduced evaluation time (5 days) was identified in Corr et al. [40], and the results did not show significant statistical differences.Reduced experimental time may lead to poor data quality or results restrictions.Furthermore, McDermott et al. [41] and McDonald et al. [42] did not carry out dietary assessment, an essential analysis that offers important results and improves the accuracy of intake.Regarding the experimental time, only Qureshi et al. [43], Hüttemann et al. [47], Si et al. [52], Gonzalez-Ruiz et al. [53], and Ramírez-Ramírez et al. [56] analyzed different time periods.Trial duration design of epicatechin supplementation is necessary, especially due to the low bioavailability of this polyphenol.Only Corr et al. [40], Mi et al. [57], and Moreno-Ulloa et al. [59] analyzed more than one dosage, providing doseresponse information and more reliable results.Concerning the plasma concentrations of epicatechin, Taub et al. [37], McDermott et al. [41], and Ramirez-Sanchez et al. [46] performed this analysis.Drug concentration in plasma provides information about the half-life of epicatechin and the plasma concentration curve.
Another factor identified as a risk factor was the different periods of euthanasia reported by Si et al. [52].Comparing the results of animals with variability in the period of euthanasia may not provide reliable data.Regarding the animal model, Si et al. [44] investigated the effects of epicatechin in db/db mice.The db/db mice have a shorter lifespan; therefore, other lineages should be considered in longevity studies.In addition, epicatechin interruption was evaluated only by Hüttemann et al. [47].The washout period aims to evaluate a substance or drug's residual effect (carry-over).Moreover, Gutierrez-Salmean et al. [48] did not report the participants' gender, which represents a limitation since gender may influence the pharmacokinetics and effectiveness of drug treatment due to hormonal actions.Lastly, no control group was identified in one article Qureshi et al. [43].Including a control group may provide a baseline in the experiment and reliable outcomes of the analyzed parameters because it validates the results of the study.
The limitations of this systematic review may be related to the search methodology used and to the restriction of the eligibility criteria.As a comprehensive view, this qualitative analysis presented a convergence of the positive effects of epicatechin on muscle growth and differentiation modulators.
Our systematic review highlights the promising potential of epicatechin in the context of muscular atrophy and its positive impacts in several biological models and systems.We recognize the need to identify gaps and guide future research directions.
When exploring the diversity of muscular atrophy models, the importance of a comprehensive characterization is crucial, considering molecular and functional nuances specific to each model.We commit to investigate additional models in order to capture a more complete picture of the effects of EC, including interactions between muscle fiber types and associated inflammatory responses.
In terms of the mechanisms involved, our current results emphasize the influence of EC in regulating protein synthesis and inhibiting muscle degradation.We agree that further investigation is crucial, with future studies focusing on elucidating specific signaling pathways, considering epigenetic aspects and intracellular inflammatory modulation.
Addressing the diversity of EC sources, is a priority that future research includes a more detailed analysis of variations in chemical compositions, aiming to better understand the specific bioactive profiles associated with each source.
We recognize the importance of randomized controlled clinical trials, committing to conducting a more rigorous review of the literature to identify and include clinical studies that meet these criteria.This will provide a more comprehensive and clinically relevant view of the effects of EC on muscle atrophy in humans.
In summary, our review, while offering valuable insights, is a starting point for future research.By addressing the questions raised, we plan to significantly contribute to the advancement of knowledge on the therapeutic application of EC in muscular atrophy.
Based on the above findings, future research prospects comprise the pressing need to establish standardized and well-defined therapeutic protocols for the administration of epicatechin in the treatment of muscle atrophy.Furthermore, conducting rigorous clinical studies with controlled and randomized designs is imperative to achieve more accurate therapeutic efficacy of epicatechin in humans.A comprehensive approach involving combined interventions, such as co-administration of epicatechin along with other therapeutic modalities, is required for further investigations.Thus, a deeper comprehension of the molecular mechanisms underlying the beneficial effects of epicatechin on muscle atrophy is essential to solidly establish clinical guidelines due to its promising application as a phytochemical "exercise pill".
Finally, it is crucial to emphasize that more evidence is needed to expand the findings of this systematic review in order to provide concrete scientific results for the therapeutic use of epicatechin.

Conclusions
This systematic review provided important evidence concerning the effects of epicatechin on the regulation of the atrogenes (FOXO, MAFbx, and MuRF1) expression and the activation of the main myogenic regulator's factors.The results evidenced the AKT/mTOR pathway signaling and mitochondrial biosynthesis induction, stimulated by epicatechin.Despite the discrepancies in the different parameters shown, the results are of great relevance due to the potential biological activities of such polyphenols.However, the scarce existing clinical studies are a barrier to validating EC'S therapeutic applicability in muscular atrophy-associated diseases.

Future Directions
Despite the biological properties of catechins, there are certain limitations for their clinical application, such as low bioavailability and degradation according to pH and temperature [87,88].Nanotechnology could contribute by promoting the stability of catechins and prolonged release [89,90].
The main challenge of nanotechnology is to develop delivery systems based on nanocarriers that target specific cells or tissues [93].Also, it is necessary to consider the advantages and drawbacks of each nanoparticle system to guarantee the effectiveness of the therapeutic actions [94] and reduce the toxic effects of polyphenol overdose, allowing greater safety in its clinical application [92].
Furthermore, it would be interesting to study the behavior of epicatechin combined with other flavonoids, such as flavocoxid, a mixture of flavonoid containing baicalin and catechin, reported in the literature as an anti-inflammatory and antioxidant bioflavonoid, in addition to inhibiting muscle necrosis and improving the regeneration and function of skeletal muscles [95,96].
The authors emphasize the need to consider factors such as EC sources, doses, bioavailability, muscle atrophy models, supplementation period, and molecular/cellular mechanisms in future studies on the use of EC in the treatment of muscular atrophy.
A detailed analysis of chemical variations between EC sources is proposed, with an emphasis on bioactive profiles.Regarding dosage, a refined approach is suggested, considering bioavailability, with the proposal of a range of effective doses.For bioavailability, the importance of exploring formulations that optimize EC absorption in target tissues stands out, including studies on pharmacokinetics, such as lipid formulations.
Concerning muscle atrophy models, a comprehensive characterization is suggested, encouraging the exploration of additional models.Regarding the duration of supplementation, long-term studies are proposed to elucidate the temporal effects of EC, addressing genetic regulation and physiological adaptations.Expanding the discussion on molecular and cellular mechanisms, including epigenetic regulation and modulation of intracellular pathways, is considered crucial.
Finally, when integrating with physical training, it is suggested to investigate the synergistic interaction between EC supplementation and different exercise modalities, exploring combined effects.Finally, the urgency of methodological standardization stands out, proposing specific guidelines for collection, analysis, and presentation of results, involving uniformity and facilitating comparisons between studies.

Figure 2 .
Figure 2. PRISMA 2020 flow diagram.Search design strategy in the databases and other sources.

Figure 2 .
Figure 2. PRISMA 2020 flow diagram.Search design strategy in the databases and other sources.**: records identified in the databases but not related to this review topic.
Failure to collect the participants' dietNutrients 2024, 16, x FOR PEER REVIEW 17 of 28

Table 4 .
Risk of bias of the studies.
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model

28 le 4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Only one dose was studied 17 of Risk of bias of the studies.
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Nutrients 2024, 16, x FOR PEER REVIEW 17 of 28

Table 4 . 4 . 4 . 4 .
Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Nutrients 2024, 16, x FOR PEER REVIEW 17 of Risk of bias of the studies.Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.N/A Difference of the euthanasia periods N/A Choice of the animal model N/A Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEW Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEW Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Absence of plasma (epicatechin) measured.
Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.
Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.
Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.N/A Difference of the euthanasia periods N/A Choice of the animal model N/A Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model

4 . 4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal modelTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated utrients 2024, 16, x FOR PEER REVIEW 17 of 28 Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.ifference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet

Table 4 . 4 . 4 . 4 . 4 . 4 . 4 . 4 . 4 .Table 4 .le 4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Participants' gender not reported Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model No control group Nutrients 2024, 16, x FOR PEER REVIEW 17 of Risk of bias of the studies.Risk of bias of the studies.

Table 4 .Table 4 .Table 4 . 4 . 4 . 4 . 28 le 4 .
one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Risk of bias of the studies.one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Risk of bias of the studies.one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Only one dose was studied 17 of Risk of bias of the studies.
ilure to collect the participants' diet N/A N/A N/A nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) measured.
Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.

Table 4 . 4 . 4 .
Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEW

4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Absence of plasma (epicatechin) measured.

17 of 28 le 4 .
Risk of bias of the studies.
ilure to collect the participants' diet nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) measured.erence of the euthanasia periods Choice of the animal model icatechin interruption was not evaluated rticipants' gender not reported No control group Reduced sample size Reduced evaluation time ilure to collect the participants' diet N/A N/A N/A nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) measured.
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.

Table 4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Nutrients 2024, 16, x FOR PEER REVIEW Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Nutrients 2024, 16, x FOR PEER REVIEW Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.N/A Difference of the euthanasia periods N/A Nutrients 2024, 16, x FOR PEER REVIEW Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods N/A N/A N/A Difference of the euthanasia periods ents 2024, 16, x FOR PEER REVIEW 17 of 28

le 4 .
ilure to collect the participants' diet nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) measured.erence of the euthanasia periods Choice of the animal model icatechin interruption was not evaluated rticipants' gender not reported No control group Reduced sample size Reduced evaluation time ilure to collect the participants' diet N/A N/A N/A nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) measured.Risk of bias of the studies.
ilure to collect the participants' diet nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) measured.erence of the euthanasia periods Choice of the animal model icatechin interruption was not evaluated rticipants' gender not reported No control group Reduced sample size Reduced evaluation time ilure to collect the participants' diet N/A N/A N/A nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) Nutrients 2024, 16, x FOR PEER REVIEW 17 of 28 Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) Nutrients 2024, 16, x FOR PEER REVIEW 17 of 28

Table 4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) Nutrients 2024, 16, x FOR PEER REVIEW 17 of Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) Nutrients 2024, 16, x FOR PEER REVIEW Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) Nutrients 2024, 16, x FOR PEER REVIEW Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet N/A Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) Nutrients 2024, 16, x FOR PEER REVIEW Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin)

Table 4 . 4 . 4 . 4 . 4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Nutrients 2024, 16, x FOR PEER REVIEW 17 of Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Nutrients 2024, 16, x FOR PEER REVIEWTable Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Nutrients 2024, 16, x FOR PEER REVIEW

28 le 4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Only one dose was studied 17 of Risk of bias of the studies.
ents 2024, 16, x FOR PEER REVIEW 17 of 28 ilure to collect the participants' diet nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) measured.erence of the euthanasia periods Choice of the animal model icatechin interruption was not evaluated rticipants' gender not reported No control group Reduced sample size Nutrients 2024, 16, x FOR PEER REVIEW 17 of 28 Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Nutrients 2024, 16, x FOR PEER REVIEW 17 of 28

Table 4 .Table 4 .Table 4 .Table 4 .Table 4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Nutrients 2024, 16, x FOR PEER REVIEW 17 of Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Nutrients 2024, 16, x FOR PEER REVIEW Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Nutrients 2024, 16, x FOR PEER REVIEW Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Nutrients 2024, 16, x FOR PEER REVIEW Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Nutrients 2024, 16, x FOR PEER REVIEW Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Reduced sample size Reduced evaluation time Failure to collect the participants' diet Only one period was evaluated Absence of plasma (epicatechin) measured.

17 of 28 le 4 .
Risk of bias of the studies.
ilure to collect the participants' diet nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) measured.erence of the euthanasia periods Choice of the animal model icatechin interruption was not evaluated rticipants' gender not reported No control group Nutrients 2024, 16, x FOR PEER REVIEW 17 of 28 Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Nutrients 2024, 16, x FOR PEER REVIEW 17 of 28

Table 4 .Table 4 .Table 4 .Table 4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Nutrients 2024, 16, x FOR PEER REVIEW 17 of Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Nutrients 2024, 16, x FOR PEER REVIEW Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Nutrients 2024, 16, x FOR PEER REVIEW Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Participants' gender not reported No control group Nutrients 2024, 16, x FOR PEER REVIEW Risk of bias of the studies.

le 4 .
ilure to collect the participants' diet nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) measured.erence of the euthanasia periods Choice of the animal model icatechin interruption was not evaluated rticipants' gender not reported Risk of bias of the studies.
ilure to collect the participants' diet nly one period was evaluated Only one dose was studied bsence of plasma (epicatechin) measured.erence of the euthanasia periods Choice of the animal model icatechin interruption was not evaluated Nutrients 2024, 16, x FOR PEER REVIEW 17 of 28 Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Nutrients 2024, 16, x FOR PEER REVIEW 17 of 28

Table 4 .
Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Nutrients 2024, 16, x FOR PEER REVIEW 17 of Risk of bias of the studies.Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Nutrients 2024, 16, x FOR PEER REVIEW Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Nutrients 2024, 16, x FOR PEER REVIEW Failure to collect the participants' diet Only one period was evaluated Only one dose was studied Absence of plasma (epicatechin) measured.Difference of the euthanasia periods Choice of the animal model Epicatechin interruption was not evaluated Nutrients 2024, 16, x FOR PEER REVIEW Abbreviations: not applicable (N/A)-Cell culture studies.Symbol in the table presents the risk of bias.

Table 1 .
Summary of the main EC supplementation parameters-Studies in humans.

Table 2 .
Summary of the main EC supplementation parameters-Studies in animals.

Table 3 .
Summary of the main EC supplementation parameters-Studies in culture cells.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.
s Taub et al.,

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.

Table 4 .
Risk of bias of the studies.