Biological Activity of Resveratrol, a Plant-Derived Polyphenol, in Combination with Orlistat: A Preclinical Study on Anti-Obesity Effects

Abstract

Resveratrol (RVT) is a plant-derived polyphenol found in traditional medicinal species such as Veratrum grandiflorum and Polygonum cuspidatum, known for their bioactive secondary metabolites. This study evaluates the anti-obesity effects of RVT alone and in combination with orlistat (OLT), a pharmaceutical lipase inhibitor, in a high-fat diet-induced obesity model in rats. Female Sprague-Dawley rats were assigned to receive RVT, OLT, a combination of both, or no treatment, over a four-week period. The combination of RVT and OLT led to a significant reduction in body weight gain and improvement in lipid profiles, including decreased LDL cholesterol. Additionally, the combination ameliorated liver enzyme elevations associated with obesity-related hepatic stress. These findings demonstrate that resveratrol potentiates orlistat’s pharmacological efficacy and highlights the therapeutic potential of bioactive compounds from medicinal plants in metabolic disease management. This study supports further development of plant-based pharmacological agents and synergistic formulations for the treatment of obesity and associated comorbidities.

1. Introduction

Medicinal plants have long served as a reservoir for therapeutic agents, many of which continue to inspire pharmacological innovation. Resveratrol (RVT), a stilbenoid polyphenol, was first isolated from the roots of Veratrum grandiflorum, a plant historically recognized for its medicinal properties [1], although numerous other species produce it in higher amounts. This traditional use underpins the modern pharmacological exploration of RVT in metabolic diseases, including obesity and diabetes. Understanding the structural analogs, derivatives, and biological activity of RVT, particularly when used in combination with other therapeutic agents, opens new avenues for its sustainable utilization and integration into modern therapeutics. Although currently extracted from sources such as grapes and Polygonum cuspidatum, resveratrol’s original discovery in Veratrum grandiflorum highlights the diverse plant-based origins of this bioactive compound and the importance of preserving the genetic diversity of such medicinal plant species [1]. Among the wide array of bioactive secondary metabolites from medicinal plants, resveratrol has emerged as a compound of significant therapeutic interest due to its anti-inflammatory, antioxidant, and metabolic regulatory properties [1].

Obesity is a global health concern with increasing prevalence, associated with various comorbidities such as cardiovascular diseases, diabetes, and dyslipidemia. While there are pharmacological treatments for obesity, they often have limitations in efficacy and tolerability. Therefore, there is a need to investigate new therapeutic strategies, including combinations of drugs that may improve outcomes. Resveratrol (RVT) is a well-known polyphenol found in various fruits and vegetables, including peanuts and grapes, and was originally extracted from Veratrum grandiflorum, a plant traditionally used in ethnomedicine [1]. In recent years, RVT has gained significant attention from medical researchers, nutritionists, and health experts due to its broad spectrum of health benefits, which include anti-angiogenesis, immune regulation, antimicrobial activity, neuroprotective effects, and potential in cancer prevention, diabetes treatment, and cardiovascular health [2,3]. These effects and RVT’s ability to reduce inflammation and oxidative stress have highlighted its role in extending lifespan across various species [4,5,6]. Moreover, RVT exhibits a favorable safety profile, with acute doses of up to 2000 mg/kg and repeated doses of 50–500 mg/kg over 28 days producing no significant adverse effects in rats [7]. Furthermore, RVT has demonstrated a capacity to improve blood glucose levels and insulin resistance in insulin-resistant rodents [8]. In other preclinical studies, RVT has been shown to attenuate weight gain in rodents fed a high-fat diet (HFD), with high doses (~400 mg/kg) enhancing energy expenditure without reducing food intake [5]. This suggests RVT exerts its effects not through calorie reduction but by stimulating metabolic processes such as the activation of the sirtuin system and enhancing energy expenditure [6,9].

Orlistat (OLT), a well-established anti-obesity drug, inhibits gastric lipase, which reduces the absorption of dietary fats and triggers weight reduction, and has demonstrated efficacy in slowing diabetes progression among high-risk individuals, although its long-term success is limited, with only 15–30% of patients achieving sustained weight loss after one year of therapy [10,11]. Moreover, OLT’s gastrointestinal side effects often limit its tolerability [10]. Given these limitations, there is increasing interest in identifying natural product-based interventions, either alone or in combination with existing pharmaceuticals, to enhance therapeutic outcomes in obesity management [4].

These two compounds exert their anti-obesity effects through distinct mechanisms: Orlistat acts by inhibiting pancreatic lipase and reducing dietary fat absorption, while resveratrol exerts multiple biological actions, including anti-inflammatory effects—particularly through modulation of lipid profiles—mitochondrial function modulation, and activation of the sirtuin 1 pathway (SIRT1), and increases energy expenditure without affecting food intake [6]. The theoretical complementarity of these actions provides a strong rationale for their combined use, which could result in enhanced efficacy or improved tolerability compared to monotherapy.

Despite the extensive research on both RVT and OLT individually, no experimental studies have yet explored the combination of these compounds in a preclinical obesity model. Using natural products such as RVT in combination with pharmaceuticals such as OLT presents an innovative approach, combining different mechanisms of action and potentially improving tolerability and efficacy. The objective of this study was to investigate the efficacy of an oral combination of RVT and OLT in controlling weight gain and its effects on biomarkers associated with obesity-related comorbidities in a rat model of HFD-induced obesity. We hypothesized that their concurrent administration could lead to greater beneficial effects on obesity-related parameters than either compound alone. This hypothesis does not assume a formal synergistic interaction but rather an additive or complementary potential arising from their distinct pharmacological profiles.

2. Materials and Methods

2.1. Animals and Diet-Induced Experimental Obesity

Female Sprague-Dawley rats 6–8 weeks old were purchased from Harlan Laboratories (Mexico) and kept under controlled environmental conditions (18–25 °C, 55–60% relative humidity, and 12 h light/dark cycles). The experiment duration, from the arrival of the animals at the laboratory to euthanasia, was 9 weeks. Prior to any procedures, the animals underwent an acclimatization period of 1 week in the housing conditions described. The animals were initially assigned to receive a regular rodent diet (ND; n = 6) (Teklad Global 2018S % Kcal: 18.0% fat, 24.0% protein, 58% carbohydrates) or a purified-ingredient high-fat diet, which resembles a “Western diet,” according to previous studies (HFD; n = 60) (TD. 88.137% Kcal: 42.0% fat, 15.2% protein, 42.7% carbohydrates) [8,9], to induce obesity by 4 weeks. This previous obesity induction allowed us to use female rats that have been reported to be a useful translational medicine tool for hormonal changes in humans due to their consistent metabolic responses, which mimic aspects of human obesity. Their hormonal profile and susceptibility to diet-induced weight gain provide valuable insights into sex-specific mechanisms. Additionally, they exhibit stable baseline metabolic rates, enhancing reproducibility in translational studies [12,13]. Then, animals on the HFD were randomly assigned to receive the active treatments for 4 weeks more. Tap water and food were supplied ad libitum. At the end of 8 weeks, the animals were euthanized through cervical dislocation, and intracardiac blood was collected to determine serum biomarkers of the lipidemic profile and hepatic damage.

All experimental procedures were conducted in strict accordance with the Mexican guideline NOM-062-ZOO-1999, Technical Specifications for the Production, Care, and Use of Laboratory Animals. The study protocol was reviewed and approved by the Institutional Animal Care and Use Committee (IACUC) of the Facultad de Ciencias Químicas, Universidad Autónoma de San Luis Potosí (protocol no. [FCQ-11-003]). All procedures were performed following internationally recognized standards for animal welfare and in compliance with the ARRIVE guidelines for the transparent and reproducible reporting of in vivo experiments.

2.2. Experimental Design

Once the rats on the HFD had reached a significant level of obesity by week 4 [14,15], they were assigned to be administered one of the following treatments (n = 6) p.o. three times daily (8 h intervals) [16]: HFD + vehicle (positive control); ND + vehicle (negative control); 3.2, 5, and 10 mg/kg OLT alone; 20, 32, and 50 mg/kg RVT alone; or 1.7/10, 3.2/20, and 5/32 mg/kg of a combination of OLT/RVT for 4 weeks. The number of animals per group was determined based on previous studies employing similar diet-induced obesity models, dosing regimens, and endpoints, which demonstrated statistically detectable differences with comparable sample sizes. No formal a priori power analysis was conducted for this study. Both OLT [16,17] and RVT [5,6] doses were selected considering previous reports of daily doses in HFD rat models that demonstrated benefits. Body weights were measured weekly during this study. With these data, % weight gain was estimated by computing the difference between the start and the end of the period of treatments (week 4 vs. week 8).

2.3. Administration of Substances

Orlistat (OLT) and resveratrol (RVT) raw materials were supplied by Laboratorios Senosiain, S.A. de C.V. (Mexico City, Mexico), due to the availability of pharmaceutical-grade material with full quality certification. The supplier had no role in the study design, data collection, or interpretation of the results. Experimental substances were prepared fresh each day by suspending the required amount of active compound in 1% carboxymethylcellulose (Sigma-Aldrich, Mexico City, Mexico). Treatments were administered orally (p.o.) three times daily via gavage using a stainless-steel feeding needle with a rounded ball tip to minimize the risk of esophageal or gastric injury. The cannula was gently inserted along the esophageal axis to avoid tracheal entry, and proper placement was confirmed prior to dosing. The administration volume was adjusted to a dosing factor of 1 mL/kg, remaining below the maximum recommended volume for rats (10 mL/kg) to prevent discomfort or aspiration. The animals were observed during and after dosing for signs of regurgitation, coughing, or distress, and all procedures followed established rodent gavage protocols to ensure reproducibility and animal welfare.

2.4. Biochemical Analysis of the Serum

Blood samples were taken at the beginning of the experiments using venipuncture from the tail vein and used together with the samples of the previous day for the evaluation of biochemical indicators. Serum samples were prepared with centrifugation of the collected blood samples (2500 rpm for 15 min) and then stored at −80 °C for biochemical determinations. The analysis of total cholesterol (CHO), HDL cholesterol (HDL), LDL cholesterol (LDL), triglycerides (TGs), total bilirubin (BIL TOT), alanine transaminase (ALT), and aspartate aminotransferase (AST) was performed in a certified clinical laboratory (UASLP, San Luis Potosí, Mexico).

2.5. Statistical Analysis

Values are expressed as the arithmetic mean ± standard error of the mean (SEM). Statistical comparisons among multiple experimental groups were performed using one-way analysis of variance (ANOVA) followed by Tukey’s multiple-comparisons post hoc test to determine differences between all treatment groups. For within-group comparisons between baseline and final values, paired t-tests were applied. Assumptions of normality and homoscedasticity were verified prior to applying parametric tests. Differences were considered statistically significant at p < 0.05. Additionally, 95% confidence intervals were calculated to provide a measure of estimate precision. All statistical analyses were conducted using StatsDirect statistical software (version 3.0, StatsDirect Ltd., Cheshire, UK).

3. Results

3.1. Anti-Obesity Effect

To evaluate the anti-obesity effect, a period of 4 weeks was set before the treatments to reach a state of obesity. The rats on the HFD became heavier at week 4 (14.2%) than those on the normal diet (8.3%; p > 0.05); this difference widened until the end of this study at week 8 (26.7% vs. 14.2%, p > 0.05). OLT and RVT alone, and a combination in three dose levels, were tested for their anti-obesity effect from week 4 onwards. Animals treated with 3.2–10 mg/kg OLT gained less weight compared to the HFD control. However, no statistical significance was achieved (Figure 1). In the case of RVT alone, a dose-dependent response was observed during the 4-week treatment (Figure 2A,B), resulting in a body weight similar to that of ND at a dose of 32 mg/kg. However, statistical significance was only achieved at the 50 mg/kg dose. With the combination of OLT and RVT, a significant effect on weight gain was observed at the two higher doses (3.2/20.0 and 5.0/32.0 mg/kg OLT/RVT). In fact, the higher dose of the combination resulted in negative weight gain, i.e., weight loss compared to ND; no other treatment was able to induce weight loss in the animals. The time dependence of the weight gain and the values at the end of the period are shown in Figure 3A,B, respectively.

3.2. Biochemical Assays

At the end of the experiments, the liver’s lipid profile was assessed and biochemical assays were performed. As shown in

Table 1. (A) Biochemical values of lipemic state after 4 weeks of treatment with OLT p.o. three times daily; (B) biochemical values of lipemic state after 4 weeks of treatment with RVT p.o. three times daily; (C) biochemical values of lipemic state after 4 weeks of treatment with OL/RVT combination p.o. three times daily.

Group	CHOL (mg/dL)		C-HDL (mg/dL)		TGs (mg/dL)		C-LDL (mg/dL)		C-VLDL (mg/dL)
	Mean	SEM	Mean	SEM	Mean	SEM	Mean	SEM	Mean	SEM
(A)
ND (basal)	84.5	1.9	33.5	2.4	105.8	25.0	25.0	7.9	66.5	3.3
HFD (basal)	95.0	6.7	30.8	0.9	108.8	15.6	41.3	6.2	53.8	2.4
HFD (final)	100.0	4.8	32.5	3.5	142.8	29.0	44.8	5.0	62.5	4.9
OLT 3.2 mg/kg	95.2	2.9	28.0	2.6	217.4	37.2	19.4	7.6	63.4	1.7
OLT 5 mg/kg	91.4	2.4	32.6	1.2	261.8 *	53.6	17.4	6.4	56.4	3.8
OLT 10 mg/kg	89.0	4.7	33.2	1.5	187.0	18.8	24.4	5.0	62.0	2.8
(B)
ND (basal)	84.5	1.9	33.5	2.4	105.8	25.0	25.0	7.9	66.5	3.3
HFD (basal)	95.0	6.7	30.8	0.9	108.8	15.6	41.3	6.2	53.8	2.4
HFD (final)	100.0	4.8	32.5	3.5	142.8	29.0	44.8	5.0	62.5	4.9
RVT 20 mg/kg	101.2	4.2	30.4	1.4	269.6 *‡	48.6	36.2	8.4	61.8	3.5
RVT 32 mg/kg	96.0	4.7	31.8	0.7	157.0	31.1	33.8	7.9	65.8	4.0
RVT 50 mg/kg	93.6	3.4	35.4	1.2	164.2	37.6	20.6	6.3	65.6	4.4
(C)
ND (basal)	84.5	1.9	33.5	2.4	105.8	25.0	25.0	7.9	66.5	3.3
HFD (basal)	95.0	6.7	30.8	0.9	108.8	15.6	41.3	6.2	53.8	2.4
HFD (final)	100.0	4.8	32.5	3.5	142.8	29.0	44.8	5.0	62.5	4.9
RVT/OLT 1.7/10 mg/kg	95.6	9.3	33.4	1.8	195.2	29.0	19.0 ‡	6.3	52.6	3.0
RVT/OLT 3.2/20 mg/kg	91.0	4.9	35.8	2.2	244.3 *†	21.1	17.4 ‡	3.3	59.8	7.9
RVT/OLT 5/32 mg/kg	86.0	4.4	35.6	1.2	201.6	26.2	9.0 †‡	3.7	55.4	4.1

* p < 0.05 vs. ND (basal); † p < 0.05 vs. HFD (basal); ‡ p < 0.05 vs. HFD (final).

A–C, there was a gradual increase in biochemical values, including GLU, HDL, LDL, and TGs, in all groups with HFD. In the case of LDL and TGs, the increase in levels appeared to reach a maximum at the end of the experiment, while CHO reached a stable level during the same period. These trends did not differ statistically.

After administration of OLT alone, the resulting biochemical values did not alter the CHO, HDL, or LDL profiles at any dose (Table 1A); however, the 5.0 mg/kg dose showed a significant increase in TG values. RVT alone showed a similar result as OLT, increasing TG levels at the lowest dose without altering the other biochemical values (Table 1B). The combination of both treatments resulted in changes in LDL and TG levels—in the first case, a dose-dependent significant decrease of about half the value of HFD. The higher dose caused a reduction in the values in the ND group. The OLT/RVT groups achieved higher TG values than the control groups (ND basal, HFD basal, and HFD final). In this case, only the 3.2/20 mg/kg OLT/RVT dose resulted in a statistical difference, as shown in Table 1C.

3.3. Hepatic Profile

At the end of the 4-week treatment, liver transaminases (TGO and ALT) and BIL were measured. The values of these three biochemical parameters were elevated during the treatment period, reaching a maximum that was almost twice as high as at the start of treatment (see

Table 2. (A) Biochemical values of hepatic damage after 4 weeks of treatment with OLT p.o. three times daily; (B) biochemical values of hepatic damage after 4 weeks of treatment with RVT p.o. three times daily; (C) biochemical values of hepatic damage after 4 weeks of treatment with RVT/OLT combination p.o. three times daily.

Group	BIL TOT (mg/dL)		TGO (I.U./L)		TGP (I.U./L)
	Mean	SEM	Mean	SEM	Mean	SEM
(A)
ND (basal)	0.04 †	0.00	139.5	21.5	47.3 †	7.0
HFD (basal)	0.08	0.01	246.5	57.7	90.3	5.1
HFD (final)	0.06	0.00	230.5	46.4	70.5	8.1
OLT 3.2 mg/kg	0.06	0.01	204.0	23.9	49.8 †	6.2
OLT 5 mg/kg	0.08 *	0.00	174.5	26.6	40.4 †	9.5
OLT 10 mg/kg	0.07 *	0.01	159.4	29.8	29.8 †	4.1
(B)
ND (basal)	0.04 †	0.00	139.5	21.5	47.3 †	7.0
HFD (basal)	0.08	0.01	246.5	57.7	90.3	5.1
HFD (final)	0.06	0.00	230.5	46.4	70.5	8.1
RVT 20 mg/kg	0.06	0.01	239.0	34.9	75.2	26.8
RVT 32 mg/kg	0.06	0.01	194.6	20.5	77.0	30.4
RVT 50 mg/kg	0.06	0.01	251.4	64.6	69.8	29.6
(C)
ND (basal)	0.04 †	0.00	139.5	21.5	47.3 †	7.0
HFD (basal)	0.08	0.01	246.5	57.7	90.3	5.1
HFD (final)	0.06	0.00	230.5	46.4	70.5	8.1
RVT/OLT 1.7/10 mg/kg	0.07	0.01	171.9	21.7	43.0 †	3.3
RVT/OLT 3.2/20 mg/kg	0.08 *‡	0.01	112.6 †	11.7	42.0 †	2.2
RVT/OLT 5/32 mg/kg	0.07 *	0.00	105.6 †	2.7	48.7	6.7

* p < 0.05 vs. ND (basal); † p < 0.05 vs. HFD (basal); ‡ p < 0.05 vs. HFD (final).

A–C for the HFD basal and HFD end group compared to the ND group). In this sense, OLT alone triggered a significant decrease in TGO and ALT levels, which appeared to be dose-dependent, although only TGO was statistically significant. Regarding BIL levels, OLT did not reverse the induction caused by HFD (Table 2A).

On the other hand, RVT alone did not alter the liver profile at any dose, as the profiles were similar in all cases (Table 2B). Nevertheless, the OLT/RVT combination significantly reduced enzyme levels. The presence of RVT in the treatment reduced the ALT and TGO produced by OLT. In the case of ALT, the reduction was statistically significant at the 1.7/10 and 3.2/20 mg/kg OLT/RVT doses, and in the case of TGO, the reduction was significant at the 3.2/20 and 5.0/32 mg/kg OLT/RVT doses.

These groups showed an obvious reversal of the enzymatic increase induced by the HFD. Strikingly, ALT levels increased at the highest dose. The combination of OLT/RVT could not reduce BIL levels at any dose. These results are shown in Table 2C.

4. Discussion

Resveratrol is a polyphenolic compound widely studied for its pleiotropic effects on metabolic regulation. Its anti-obesity actions are primarily linked to activation of the sirtuin 1 pathway (SIRT1), enhancement of mitochondrial biogenesis, and modulation of AMP-activated protein kinase (AMPK) signaling, resulting in increased energy expenditure and improved insulin sensitivity [5,6]. Orlistat, in contrast, exerts its therapeutic effects through irreversible inhibition of gastric and pancreatic lipases, thereby reducing the hydrolysis and absorption of dietary triglycerides [18]. The complementary mechanisms of these agents—one targeting nutrient absorption and the other enhancing energy metabolism—provide a pharmacological basis for the observed metabolic improvements in the combined treatment group. This mechanistic rationale aligns with the growing interest in multi-targeted approaches to address the complex pathophysiology of obesity.

In the present study, the ability of a combination of ORL and RVT in a fixed ratio to control diet-induced obesity in Sprague-Dawley rats was investigated. This model has been used as a tool to evaluate different types of treatments for obesity and related diseases due to the pathological state it induces in the animals using a therapeutic approach instead of the commonly used prophylactic approach [18,19]. The dietary profile in this study increased calories from fat (from 18% in the ND to 42.0% in the HFD), resulting in an induction of obesity prior to treatments. ORL is considered a pharmacological therapy for the treatment of obesity and related diseases [20]. At the same time, controversy exists in the case of RVT, as it is a dietary supplement with various non-specific therapeutic effects [21].

We observed that all combination doses led to less weight gain than in the HFD group. Considering the weight gain in the positive control as the maximum observed effect (Emax of obesity), the anti-obesity effect of the treatments can be estimated as the fraction of the Emax. Using this variable, it was estimated that the higher dose of the ORL/RVT combination achieved an anti-obesity effect of approximately 127%, significantly higher than the 24% of ORL or 87% of RVT alone. This effect at the higher doses of the ORL/RVT combination exceeded the algebraic sum of the individual components, indicating a likely synergism in the anti-obesity effect of the combination. This is to be expected, as two compounds with anti-obesity properties and different mechanisms of action and therapeutic targets are combined, which could elicit the pharmacological response, especially if one of them is from natural sources such as RVT [20,21]. However, this study was not designed to demonstrate synergism, so further studies need to be conducted in the future. Additionally, no formal a priori power analysis was conducted. The chosen sample size was based on prior studies employing comparable rodent models, treatment durations, and endpoints, which had demonstrated statistically detectable effects with similar group sizes. This limitation should be considered when interpreting the results, and future studies should include a formal power calculation to ensure optimal study design. Additional parameters such as rodent BMI, visceral fat quantification, liver/body weight ratio, glucose, insulin, CRP, and hepatic or renal biochemical markers were not assessed. Future studies including these endpoints could provide a more comprehensive metabolic profile.

The present findings expand upon previous evidence by suggesting that the combined administration of OLT and RVT may exert additive or complementary effects on key metabolic pathways involved in obesity-related disorders. Beyond the reduction in weight gain, the combination demonstrated favorable trends in lipid metabolism, hepatic biomarkers, and LDL cholesterol modulation, which may be partly explained by the distinct but converging mechanisms of action of both agents. This interpretation aligns with prior reports on OLT’s inhibition of dietary fat absorption via gastric and pancreatic lipase blockade [20], and RVT’s pleiotropic modulation of energy homeostasis and oxidative stress [6,21,22]. Together, these actions may enhance lipid clearance, attenuate hepatic steatosis, and improve systemic metabolic regulation in diet-induced obesity.

Although the combination therapy showed greater efficacy than either agent alone, this study was not designed to formally evaluate pharmacodynamics synergies (e.g., by isobolographic or combination index analysis). Therefore, although a synergistic interaction is plausible, future studies are needed to confirm this hypothesis with validated models of drug interaction.

At the molecular level, RVT is known to activate SIRT1, promote mitochondrial biogenesis, and modulate inflammatory pathways, while OLT primarily acts through gastrointestinal lipase inhibition, reducing the intestinal absorption of triglycerides and cholesterol. The concurrent targeting of these complementary pathways may result in enhanced metabolic benefits, although the present study did not employ formal synergy analyses such as isobolographic evaluation or combination index methods. Furthermore, the relatively small sample size and the use of a single animal model limit the generalizability of these findings, underscoring the need for further studies with broader experimental designs to confirm the mechanistic interplay between these agents.

On the other hand, previous reports have suggested that both OLT and RVT contribute to the control of dyslipidemia [6,20,23]. Given that CHO, C-LDL, and TGs increased when rats were administered HFD, we found that no treatment alone was able to significantly reduce these levels. Notwithstanding, the combination of OLT and RVT reduced C-LDL levels, a predictive factor for atherosclerosis, which is consistent with Lagouge et al. in 2006 [6], who demonstrated that RVT has anti-dyslipidemic activity in obesity. Assuming that RVT activates the sirtuin system and OLT inhibits gastric lipase, this could reduce lipemia and accelerate lipid metabolism, which could explain the LDL lowering via inhibition of mitochondria-induced oxidative stress [24]. Another important finding was that TG levels were increased in the OLT group (3.2, 5, and 10 mg/kg) compared to the HFD group. In this sense, previous studies reported that doses below 10 mg/kg resulted in an improvement in weight gain but an increase in TG levels, probably due to interindividual variations and a weak effect on this parameter [25], while higher doses (30 and mg/kg) improved TG levels in about 65% [26], whereas in our doses they increased by 83%, showing that the effect is only visible at high doses of OLT alone [27,28].

Furthermore, the present study demonstrated that although an HFD led to an increase in liver transaminases and BIL (this effect is considered an indicator of liver damage), no treatment was able to induce a worsening of this condition, except in the case of BIL, for which all treatments seem to induce higher values. The study by Lagouge et al. in 2006 [6] describes how RVT increases hepatic mitochondrial activities and citrate synthase, an indicator of aerobic metabolism. In the experiments of the present study, no overt clinical signs of liver damage or behavioral alterations were observed; however, more detailed histological and biochemical analyses would be required to confirm the absence of hepatic injury. The ethnobotanical origin of RVT from Veratrum grandiflorum highlights the importance of conserving medicinal plant species that serve as the basis for modern pharmaceuticals. While RVT is often synthesized or extracted from grapes and peanuts today, its traditional use underscores the relevance of documenting and preserving local knowledge on medicinal plant use. The potential therapeutic synergy observed in this study also supports the continued exploration of plant-derived bioactives from diverse sources, particularly those at risk due to overharvesting or habitat degradation. Biotechnological strategies, such as microbial synthesis or controlled cultivation of RVT-producing species, could mitigate pressure on wild populations. The observed synergistic effect of RVT and OLT supports the exploration of natural–synthetic combinations for improved therapeutic efficacy. The pharmacological validation of resveratrol, a well-characterized polyphenol from medicinal plants, underscores the continued relevance of botanical sources in modern drug development.

The highest dose of resveratrol tested in our rat model (50 mg/kg/day) corresponds to a human equivalent dose (HED) using body surface area normalization of about 8 mg/kg/day or about 480 mg/day for a 60 kg adult [17,28]. This scaling method is generally accepted for preliminary dose translations and supports the clinical feasibility of combination therapy in humans.

5. Conclusions

The present study demonstrates the potential efficacy of resveratrol (RVT) and orlistat (OLT) in controlling diet-induced obesity in a preclinical model using Sprague Dawley rats. The combination of RVT and OLT, particularly at higher doses, significantly reduced weight gain, with some doses even inducing weight loss. This suggests a possible synergistic effect between the two compounds, surpassing the efficacy of each agent when used alone. Moreover, the combination treatment improved lipid profiles, notably reducing LDL levels, a key predictor of atherosclerosis, while the effect on triglycerides (TGs) was more variable and required further investigation. While RVT’s established role in regulating metabolism and reducing oxidative stress, combined with OLT’s inhibition of fat absorption, appears to explain the observed benefits, further studies are necessary to confirm whether the interaction between these compounds is synergistic. Additionally, this study highlighted the tolerability of the treatments, with no significant liver toxicity observed. However, elevated bilirubin levels and variations in liver enzyme activity warrant further exploration to assess any long-term hepatic effects. Overall, the findings suggest that the combination of OLT and RVT represents a promising therapeutic strategy for controlling obesity and its associated comorbidities.

Translating these findings into potential human applications, the highest tested dose of RVT (50 mg/kg/day in rats) corresponds approximately to a human equivalent dose (HED) of 8 mg/kg/day, or 480 mg/day for a 60 kg adult, according to standard interspecies scaling. This dose is within the range used in human supplementation studies, suggesting that the combination therapy could be clinically feasible and merits further exploration in human trials.

These findings further highlight the value of integrating traditional plant knowledge with modern pharmacological strategies and stress the importance of conserving biodiversity to ensure the sustainable supply of medicinally important phytocompounds such as resveratrol.