Lipidology

Milk fatty acid (FA) synthesis and enteric methanogenesis share common biochemical pathways related to rumen fermentation patterns and microbial volatile FA production. The FA profile of milk is known to correlate with methane (CH₄) emissions; thus, FA profiling has been proposed as an indirect method to predict CH₄ emissions from dairy cattle. This study aimed to (1) investigate the milk FA profiles of Holstein cows to identify candidate biomarkers for predicting CH₄ output (g/d), CH₄ yield (g/kg dry matter intake), and CH₄ intensity (g/kg energy-corrected milk), and (2) develop and compare regression models predicting CH₄ emissions. Forty-eight cows, fed industry standard diets, were enrolled in an exploratory trial. Milk samples and CH₄ measurements were collected thrice per day, and intake was recorded daily. Milk lipids were extracted, transesterified, and subsequently analyzed via gas–liquid chromatography. Three penalized regression models were compared for predicting CH₄ emission metrics using milk FAs and management variables. Methane emission metrics corelated positively with short- and medium-chain FAs, polyunsaturated FAs, and branched-chain FAs, while monounsaturated FAs correlated negatively. Notably, this study observed novel correlations between 11-cyclohexyl-11:0; and 20:3 c5,c8,c11 and CH₄ metrics (|r| = 0.58–0.79). Across all CH₄ metrics, the models demonstrated high predictive accuracy (R² = 0.71–0.87; concordance correlation coefficient = 0.83–0.93). The findings of this study indicate that milk FA profiling may be an effective method to detect CH₄ emissions from cows fed industry standard diets and highlight the need for further refinement of prediction models. Full article

Background/objectives: Plant-based meat analogues (PBMAs) are designed to mimic meat products and to be cooked under similar conditions by consumers. There have been few studies into the lipid stability of PBMAs, and no published studies have investigated the effect of cooking on the lipid stability of PBMAs. Methods: This study analysed the effect of recommended cooking conditions on the lipid oxidation of three commercial chicken schnitzel PBMAs with differing fatty acid composition. Fatty acids and lipid classes were analysed using gas chromatography (GC) and capillary chromatography (Iatroscan) with flame ionisation detectors, respectively. Lipid oxidation was analysed using multiple tests, including peroxide value (POV), p-Anisidine value, acid value, and thiobarbituric acid reactive substance (TBARS) tests, which then allowed for the total oxidation (TOTOX) to be calculated. Results: Fatty acid analysis by GC showed different levels of saturated and unsaturated fatty acid contents in all PBMAs, with oleic acid (C18:1) being the most abundant (product A = 52%; product B = 62%; product C = 37%). Meanwhile, lipid class analyses by Iatroscan revealed that the oils used in the PBMAs were composed of triacylglycerol (TAG), which remained intact after cooking. Lipid oxidation tests showed no major increases between the raw and cooked PBMA. Also, the TOTOX values for each product did not increase significantly (p < 0.05) due to cooking (TOTOX values for raw/cooked product A = 9.36/9.99; product B = 5.88/6.19; product C = 11.31/11.92), suggesting a broad stability of the lipids. Conclusions: Therefore, if the on-package cooking instructions are followed for these three PBMA products, their lipid oxidation levels remain within safe limits. Full article

Background: Familial hypercholesterolemia (FH) is a monogenic disorder causing markedly elevated low-density lipoprotein cholesterol (LDL-C) and premature atherosclerosis. Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme in antioxidant defense via NADPH production. G6PD deficiency, an X-linked disorder impairing redox homeostasis, may contribute to cardiovascular disease (CVD) risk. This study examined whether G6PD deficiency increases CVD risk in FH patients. Methods: We retrospectively analyzed 217 FH patients. Clinical data included demographics, lipid profiles, G6PD status, and atherosclerotic CVD outcomes (coronary, cerebrovascular, or peripheral arterial disease). In a subset, FH was confirmed by LDLR gene sequencing, and G6PD Mediterranean and Seattle variants were genotyped. Cumulative CVD prevalence was compared between G6PD-deficient and G6PD-normal FH patients. Multivariable logistic regression was adjusted for age, sex, body mass index, high blood pressure, and smoking. Results: Participants (mean age 47 years, 60% female) had markedly elevated LDL-C (mean 292 mg/dL at diagnosis). Atherosclerotic CVD was present in 119 (55%) patients. G6PD-deficient FH patients had a significantly higher CVD prevalence than those with normal G6PD activity (77.4% vs. 39.8%, p < 0.0001). LDL-C levels were higher in the G6PD-deficient group than in the non-deficient group, and this difference reached statistical significance in the univariate analysis. In the multivariable analysis, G6PD deficiency remained an independent CVD predictor (adjusted OR 3.57, 95% CI 1.30–9.83) after controlling for conventional risk factors. Conclusions: In FH, hereditary G6PD deficiency is associated with a markedly increased risk of atherosclerotic CVD. A pro-oxidative state in G6PD-deficient FH patients may play a role in premature atherogenesis. G6PD status may represent a cardiovascular risk modifier in FH, warranting further research into underlying mechanisms and targeted management. Full article

This systematic review examines the impact of vegetable oil consumption, such as extra virgin olive, olive, soybean, palm olein, corn, and camellia seed oils, on both human and animal health, alongside factors influencing oil quality and safety. A variety of studies were included, such as clinical trials, cohort studies, animal experiments, and reports on production methods and contamination (polycyclic aromatic hydrocarbons (PAHs) and heavy metals). The literature search was performed in scientific databases indexed up to September 2025, and risk of bias was assessed using specific tools appropriate for each study design. The findings suggest that, among the oils studied, extra virgin olive oil showed the most consistent benefits, including improvements in endothelial function, lipid profiles, weight management, and reduced mortality in humans. Animal studies corroborate hepatoprotective effects and weight regulation benefits. Oil quality is influenced by genetic, environmental, and technological factors, including cultivar selection, pollination, post-harvest handling, and extraction techniques (cold, hot, DIC, MFA, encapsulation) and refining processes, which can affect both nutritional benefits and contaminant levels. Although contaminants such as PAHs and heavy metals (Cd, Pb, As) are generally below regulatory thresholds, some contexts may present health risks. High-quality vegetable oils confer cardiovascular, metabolic, and hepatic benefits. However, their contribution to public health relies on strict production practices, continuous monitoring of contaminants, and the implementation of technological innovations to ensure both safety and optimal health outcomes. Full article

ATP citrate lyase (ACL) is a highly conserved enzyme across eukaryotes that catalyzes the generation of cytosolic acetyl-CoA from citrate—a pivotal step linking central carbon metabolism to lipid biosynthesis. In the oleaginous yeast Yarrowia lipolytica, ACL is encoded by two genes, ACL1 and ACL2, forming a heteromeric complex that mirrors the multidomain architecture of the single-chain ACL enzymes found in mammals and plants. This conservation of catalytic architecture reflects a shared catalytic strategy across kingdoms, underscoring ACL’s fundamental role in metabolic integration. In Y. lipolytica, ACL is essential for directing mitochondrial citrate toward acetyl-CoA production and subsequent lipid accumulation. Yet, in contrast to well-characterized ACLs in animals and plants, the functional mechanisms and regulation of yeast ACL remain incompletely understood. A deeper understanding of ACL in Y. lipolytica offers not only evolutionary insights but also potential avenues for engineering lipid overproduction in microbial systems. Full article

In the last twenty years, an increasing volume of research has characterized lipids as dynamic signaling molecules that play essential roles in various physiological and pathological processes, especially concerning chronic diseases such as cardiovascular disorders, diabetes, liver disease, neurodegeneration, cancer, obesity, diabetic and chronic kidney diseases and atherosclerosis. Dysregulation of lipid synthesis and storage, lipolysis, fatty acid oxidation, lipid signaling pathways, and organelle-specific lipid modifications, including mitochondrial phospholipid remodeling and endoplasmic reticulum stress induced by saturated fatty acids, are recognized as contributors to the initiation and progression of this pathogenesis. Concurrently with the increasing comprehension of lipid metabolism, the last decade has seen progress in the understanding of genome control, especially with non-coding RNAs (ncRNAs). MicroRNAs, long non-coding RNAs, and circular RNAs, as ncRNAs, are essential modulators of gene expression at the epigenetic, transcriptional, and post-transcriptional levels that affect a number of lipid metabolism-related processes, such as fatty acid synthesis and oxidation, cholesterol homeostasis, and lipid droplet dynamics. Therapeutically, ncRNAs hold considerable promise owing to their tissue specificity and modularity, with antisense oligonucleotides and CRISPR-based editing currently under preclinical evaluation. In this context, we review recent studies exploring the interplay between ncRNAs and the regulatory networks governing lipid metabolism, and how disruptions in these networks contribute to chronic disease. This emerging paradigm underscores the role of ncRNA–lipid metabolism interactions as central nodes in metabolic and inflammatory pathways, highlighting the need for a holistic approach to therapeutic targeting. Full article

Background: Dyslipidaemia promotes atherosclerotic plaque formation. Plaques that are vulnerable to rupture have a higher proportion of inflammatory (M1:CD86) macrophages in their cap. Many plaque macrophages are derived from blood monocytes which have been exposed to elevated blood lipid levels. Here, we explored whether the inflammatory state of monocyte-derived macrophages is associated with blood lipid levels and assessed whether oxidised low-density lipoprotein (oxLDL) directly induces some of the observed changes. Method: Blood was collected from 20 individuals. Lipid profiles were measured, and monocytes differentiated into macrophages. Macrophage inflammatory state was assessed by flow cytometry for phenotypic markers (e.g., CD86 and CD163) and cytokine production: TNF, IL-1β, and IL-6. Furthermore, monocytes were isolated from 6 normo-lipidaemic individuals and cultured with oxLDL, followed by stimulation with LPS/IFNγ and assessment of the cytokine response. Results: The inflammatory phenotype acquired by macrophages (ex vivo) was related to levels of in vivo circulating lipids. Correlations for CD86/CD163 were found with CVD risk markers; most strongly with triglycerides (TG) and TG/HDL-C, but also with cholesterol/HDL-C and ApoB/ApoA1 and inversely with LDL particle size. Functionally, macrophage production of inflammatory cytokines (TNF and IL-1β) correlated with oxLDL levels and inversely with ApoA1. Macrophages differentiated from monocytes cultured with oxLDL produced significantly higher IL-1β but lower IL-10 (in response to LPS/IFNγ), compared to control cells. Conclusions: Monocyte-derived macrophages adopt an inflammatory phenotype relative to the levels of circulating lipid factors that are characteristic of atherogenic dyslipidaemia (such as high TG, TG/HDL-C and low LDL particle size), but not LDL-C. Full article

It has long been recognized that elevated circulating lipid levels are among the strongest risk factors for the development of plaques within the arterial wall that are characteristic of atherosclerotic cardiovascular disease. Indeed, decades of studies have identified the deposition of low-density lipoprotein as an initiator of this disease, which coordinates the vascular and immune dysfunction that fuels the advancement of the atherosclerotic plaque. However, in the vessel wall, deposited cholesterol and fatty acids are dynamic in nature and engage signaling pathways. Shifting from metabolic-related pathways, lipid modifications and their conversion to intermediates engage signaling cascades that further perpetuate the inflammatory milieu of the atherosclerotic plaque and its progression towards the fatal end-stage events associated with cardiovascular disease, including myocardial infarction. In this review, we will cover the cellular and molecular mechanisms that preserve homeostasis and advance disease, including how lipid species induce endothelial dysfunction and drive the development of macrophage foam cells. We will additionally discuss ongoing therapeutic strategies to combat the hyperlipidemia that underlies atherogenesis. Full article

Lipid droplets are the neutral lipid storage compartments of eukaryotic cells. Mitochondria are the main source for ATP, which is generated through oxidative phosphorylation. Thus, both organelles play essential roles in fatty acid metabolism and energy homeostasis. Therefore, functional and physical interaction of lipid droplets with mitochondria is of special importance as essential processes, such as lipolysis, triacylglycerol synthesis, thermogenesis or the protection against oxidative stress, and lipotoxicity, depend on cooperation of these two organelles. Physical interaction of LDs with mitochondria is mediated by specific molecular complexes at inter-organelle membrane contact sites. Substantial progress has been achieved during the last decade in understanding the formation and the structural components of lipid droplet–mitochondria contact sites. This review gives a brief overview of the different molecular complexes that have been identified in different mammalian cell types under different conditions and their regulation. Full article

Background: Achilles tendon (AT) thickening reflects cumulative low-density lipoprotein cholesterol (LDL-C) exposure. The Japan Atherosclerosis Society (JAS) explicitly includes AT thickness as a diagnostic criterion for familial hypercholesterolemia (FH) in adults, whereas internationally, it is not a standard diagnostic measure. However, the clinical significance of AT thickening in pediatric populations remains unclear. Methods: We conducted a single-center, retrospective, observational study involving pediatric patients (11–18 years old) with suspected FH through standardized universal lipid screening across Kagawa Prefecture, Japan. Genetic testing confirmed FH through pathogenic variants in the LDLR, PCSK9, or APOB genes. The AT thickness was measured using a standardized ultrasonography protocol. We assessed associations between the FH status, cumulative LDL-C levels, and AT thickness. Results: In the pediatric patients, no significant difference in the AT thickness was observed between the FH and non-FH groups (median 4.4 vs. 4.5 mm; p = 0.570). Cumulative LDL-C was higher in the FH group, while no clear association between cumulative LDL-C and AT thickness was apparent in either group. Conclusions: In this single-center, retrospective study of pediatric patients identified through standardized universal lipid screening, no significant differences were found in AT thickness between FH and non-FH groups although cumulative LDL-C levels were higher in the FH group. Given methodological limitations (small sample size, selection bias, and residual confounding related to statin therapy and growth), these findings should be interpreted as exploratory rather than confirmatory. Regardless of genotype, early risk management may be warranted. Full article

Background and aim: ANGPTL3 is a hepatokine acting as a negative regulator of lipoprotein lipase (LPL) through its N-terminal domain. Besides this activity, the C-terminal domain of ANGPTL3 interacts with integrin αVβ3. Since integrins are involved in inflammation and in the initiation of atherosclerotic plaque, the aim of our study was to evaluate the potential direct pro-inflammatory action of ANGPTL3 through the interaction of the fibrinogen-like domain and integrin αVβ3. Methods: We utilized cultured THP-1 human-derived macrophages and evaluated their pro-inflammatory phenotype in response to treatment with human recombinant ANGPTL3 (hANGPTL3). By Western blot, RT-qPCR, biochemical analysis, and ELISA assays, we determined the expression of genes and proteins involved in lipid metabolism and inflammatory response as well as intracellular cholesterol and triglyceride levels. In addition, we evaluated the effect of hANGPTL3 on the cellular cholesterol efflux process. Results: Incubation of THP-1-derived macrophages with 100 ng/mL of hANGPTL3 increased the mRNA expression of the pro-inflammatory cytokines IL-1β, IL-6, and TNFα (respectively, 1.87 ± 0.08-fold, 1.35 ± 0.11-fold, and 2.49 ± 0.43-fold vs. control). The secretion of TNFα, determined by an ELISA assay, was also induced by hANGPTL3 (1.98 ± 0.4-fold vs. control). The pro-inflammatory effect of hANGPTL3 was partially counteracted by co-treatment with the integrin αVβ3 inhibitor RGD peptide, reducing the mRNA levels of IL-1β (3.35 ± 0.35-fold vs. 2.54 ± 0.25-fold for hANGPTL3 vs. hANGPTL3 + RGD, respectively). Moreover, hANGPTL3 reduced cholesterol efflux to apoA-I, with a parallel increase in the intracellular triglyceride and cholesterol contents by 31.2 ± 2.8% and 20.0 ± 4.1%, respectively, compared to the control. Conclusions: ANGPTL3 is an important liver-derived regulator of plasma lipoprotein metabolism, and overall, our results add a new important pro-inflammatory activity of this circulating protein. This new function of ANGPTL3 could also be related to triglyceride and cholesterol accumulation into macrophages. Full article

Introduction: Gynoid lipodystrophy (GL) affects most women, manifesting itself from puberty to adulthood. Its multifactorial etiology generates controversy in the literature about the most suitable treatment. Several methods are used, from the smallest to the most invasive, in the search for an effective fight against the severity of GL. The positive effect of ultrasound therapy (US) in decreasing subcutaneous adipose tissue is in increasing the skin permeability of pharmacological molecules, and it has aroused interest in the effect of a combination of the two techniques on the severity of GL. However, the results of this technique associated with an exercise program are unknown. Objective(s): To analyze the effect of three sessions of US + 5% caffeine in association with the realization of an exercise program, in females, on the level of severity of GL in the gluteal region and on the posterior proximal third part of the thigh. Methods: A total of 36 healthy women, aged between 18 and 55, who were considered to have GL, were randomly allocated in two experimental groups and one placebo group. The placebo group (PG) performed only physical exercise during the study. Experimental group 1 (EP1) performed US with 5% caffeine alongside a physical exercise protocol and experimental group 2 (EP2) performed US with a conventional US gel alongside a physical exercise protocol. The three groups completed three intervention sessions over 3 weeks, with one session per week. In addition to the level of severity assessed by the Cellulite Several Scale (CSS), anthropometric measures, body composition, and lipid profile of the participants were evaluated. The first assessment was carried out before the intervention (M0) and the last assessment after the three interventions (M1). The results were analyzed using the ANOVA test. The Tukey test was used for multiple comparisons of the groups in all variables, except for those related to the CSS, where the Kruskal–Wallis test was used with a significance level of 0.05. Results: A total of 29 women completed the study. There was a significant decrease inside the PG related to triglycerides (p = 0.012). In M1, all groups started to present median values below 200 mg of triglycerides. In cholesterol, a significant reduction was observed in all groups (p = 0.05). On the gluteal level at 5 cm, there was a decrease in EP1 and EP2 between M0 and M1 with p = 0.006 and p = 0.002, respectively. On the CSS there were no significant differences between groups or between moments. Conclusions: Three sessions of 5% caffeine and US in association with a physical exercise protocol have no effect on reducing the level of severity of GL. Full article

Microbial lipids are substances of high added value produced by single-cell organisms grown on simple substrates. These lipids, depending on the producing organism, may contain rare fatty acids, whose isolation and purification from non-microbial sources usually is an inefficient and costly procedure. Such fatty acids mostly include members of the omega-3 and omega-6 families of polyunsaturated fatty acids, which are credited with potential anticancer, anti-inflammatory, cardioprotective, and neuroprotective actions. However, their poor solubility in aqueous solutions often restricts their potential applications, as routes other than dietary consumption are unavailable. A promising approach for administering them is their conversion into alkali salts, mostly with lithium or potassium, which are water-soluble and bio-assimilable. In this article, all studies investigating the potential anticancer effects of alkali salts of fatty acids isolated from microorganisms were reviewed in an attempt to sum up existing knowledge and encourage further research. Full article

In the first part of this paper, we introduce the marine copepod Calanus finmarchicus, its lifecycle and ecology, and describe the technologies developed for harvesting and extracting oil from this copepod. Calanus oil has a unique composition, with its fatty acids—including a high concentration of long-chain omega-3 polyunsaturated fatty acids (PUFAs) and monounsaturated fatty acids (MUFAs)—bound to long chain fatty alcohols in the form of wax esters. In the second part of this paper, we review pre-clinical and clinical studies conducted over the last two decades, which demonstrate the potential health benefits of Calanus oil. These studies highlight its role in preventing obesity-related metabolic distortions, such as inflammation and reduced insulin sensitivity. Full article

Background/Objectives: Recent studies show that the gut microbiome plays a pivotal role in the (patho)physiology of metabolic dysfunction-associated steatotic liver disease (MASLD), likely via metabolites they produce that are transported via the portal vein towards the liver where they first encounter liver sinusoidal endothelial cells (LSECs). LSECs may modulate the effects the gut microbes have on the liver, e.g., on the progression of MASLD. Methods: This review aims to describe the current knowledge on the role of LSECs in mediating the effect of gut microbial products in MASLD. Results: Various studies show that LSECS have a contributing role in MASLD pathogenesis, suggesting that proper LSEC functionality is required to protect the liver from gut-driven attacks. Conclusions: Dedicated studies on the role and effects of gut-derived molecules on LSEC functionality are lacking, likely because such studies depend on labor-intensive techniques such as scanning electron microscopy (SEM). Full article

Background: Neem seed oil (Azadirachta indica A. Juss) is widely used in the pharmaceutical, agricultural, and food industries due to its antiseptic, fungicidal, pesticidal, and antioxidant properties, attributed to over 300 bioactive compounds and a high content of unsaturated fatty acids. Methods: This study aimed to characterize a commercial sample of neem oil regarding its physicochemical properties and identity profile, using official methodologies from the American Oil Chemists’ Society (AOCS), and to compare the results with literature data. Results: The sample exhibited the following parameters: free fatty acids (2.0 ± 0.02%), acidity index (3.9 ± 0.04 mg KOH/g), peroxide value (3.2 ± 0.1 mEq/kg), iodine value (116 ± 12 g I₂/100 g), and saponification index (198 ± 8 mg KOH/g). The predominant coloration was yellowish, with total chlorophyll and carotenoid levels below the equipment’s quantification limits. Fatty acid composition was mainly long-chain (C16–C18), with notable levels of linoleic acid (46%), oleic acid (28%), palmitic acid (12%), linolenic acid (5.5%), and stearic acid (4.1%). The triacylglycerol profile showed a predominance of triunsaturated (51%) and diunsaturated species (41%). Differential scanning calorimetry (DSC) analysis revealed crystallization events between −6 °C and −57 °C and fusion events between −44 °C and −1 °C, consistent with the high unsaturation level of the lipids. Conclusions: The analyzed neem oil sample meets quality and identity criteria, making it suitable for various industrial applications. The characterization confirms its potential and aligns with literature data, emphasizing its relevance for industrial use. Full article

Background: Adipose tissue growth follows a biphasic process involving both cellular hyperplasia (an increase in adipocyte number) and hypertrophy (an increase in adipocyte size). Rumen-protected fatty acid supplements have been utilized to alter fat deposition, modify the fatty acid composition of meat, and reduce methane emissions. However, limited research has explored how different fatty acid mixtures influence adipose tissue’s biphasic growth phases. Methods: The objectives of this study are to investigate the effects of fatty acid mixtures (seven different mixtures) on: (1) hyperplasia of undifferentiated stromal vascular fraction (SVF) cells, or (2) hypertrophy of chemically differentiated SVF cells isolated from subcutaneous adipocytes of finished steers. Results: Mixtures containing palmitic and linoleic acids stimulated hyperplasia, enhancing the proliferation of undifferentiated SVF cells, while mixtures with oleic acid (50%) predominantly promoted hypertrophy, driving lipid accumulation and adipocyte maturation. Conversely, mixtures composed solely of saturated fatty acids (50% palmitic and 50% stearic acids) exhibited a profound inhibitory effect on both hyperplasia and hypertrophy, underscoring the importance of fatty acid composition in regulating adipogenesis. Conclusions: These findings demonstrate that the composition of fatty acid mixtures directly influences adipogenesis and lipogenesis in vitro, highlighting their potential role in designing tailored rumen-protected supplements for modifying fat deposition in livestock. Full article

(1) Background: Musculoskeletal trauma from combat wounds, accidents, or surgeries is highly associated with infections and hospitalization. The current “gold standard” for such injuries when access to hospitals is limited is administering antibiotics and opioids; however, they are not ideal treatments due to their contributions to antibiotic resistance and the opioid epidemic. Electrospun chitosan acylated with lipids and loaded with hydrophobic drugs has been shown to release the therapeutics systemically and to prevent infections. (2) Methods: Electrospun chitosan membranes (ESCMs) were fabricated and acylated using decanoyl chloride. FTIR was used to confirm acylation through the presence of ester bonds and acyl chains. ESCMs were loaded with the quorum-sensing molecule cis-2-decenoic acid (C2DA) and the local anesthetic bupivacaine and then implanted in rat femurs for 3 days. Afterward, the rats were euthanized, and CFUs were measured on retrieved bone, tissue, and treatment material. (3) Conclusions: While ESCMs prevented bacterial growth on the surface of the material, controls outperformed treatment groups. This is possibly due to bupivacaine’s role in inhibiting sodium channels, which favors the production of Th2-type cytokines associated with immune response suppression. Furthermore, ESCMs provide a large surface area for bacteria to grow on and form bridges between nanofibers. Full article

Background: Genetic selection and improved nutrition and management practices have transformed the Holstein cow. Objectives: This study examined the impacts of 50 years of selection on milk composition during early lactation by comparing milk from contemporary Holsteins (CH) and a unique population of unselected Holsteins (UH) that produce less than half as much milk as their CH herdmates. Methods: Multiparous UH and CH cows (n = 12/genotype) were housed in the same facility, fed the same diets and subjected to the same management procedures. Milk samples were collected weekly through to week 9 of lactation. The proximate composition of milk was determined by infrared spectroscopy and its lipidome by liquid chromatography–mass spectrometry and structural analysis. Data were analyzed as repeated measures using mixed-model procedures with the week of lactation as the repeated effect. Results: An energy balance nadir occurred at week 1 for UH and CH cows but was more severe (−4.5 vs. −14.8 Mcal net energy per day, respectively) for the CH cows. Lipidomic comparison of the 50 most abundant triacylglycerols (TAGs) revealed that CH milk had more TAGs with at least two preformed fatty acids and fewer TAGs with at least two de novo synthesized fatty acids than UH milk. Fatty acid analysis revealed that the increase in preformed fatty acids in CH cows was responsible for the different TAG profiles in UH and CH milk. Furthermore, CH milk contained less free carnitine, short-chain acylcarnitines and lactic acid but more butyric and 3-hydroxybutyric acid than UH milk in early lactation. Conclusions: These results demonstrate that differences in energy balance were primarily responsible for the differences in milk composition between the UH and CH genotypes in early lactation. Full article