In animal models, EPA and DHA have been shown to exert beneficial effects against obesity. For instance, animals that are fed a DHA or EPA diet have been shown to experience weight loss or decreased adipose tissue mass (60–62). Specifically, HFD-fed mice that received 1% DHA or 4% EPA supplementation exhibited body weight loss (60). Furthermore, in another research, the administration of EPA/DHA reduces visceral adipocyte size as well as adiposity induced by HFD (61). Supplementation with EPA and DHA in the context of a HFD reduced lipid accumulation in both brown adipose tissue (BAT) and white adipose tissue (WAT) in C57BL/6J mice (63). These positive effects are attributed to the fact that EPA and DHA benefit lipid homeostasis, adipocyte function, and leptin and adiponectin production (62).

Although DHA and EPA supplementation pose beneficial effects for obesity in animal models, this effect remains rather multidimensional in humans (64, 65). Meta-analyses have shown that n-3 PUFA does not affect weight loss or BMI; however, it may provide benefits by reducing waist circumference and TG level in obese adults (64, 65).

According to the Global Burden of Disease 2019 report, a diet low in n-3 PUFAs is associated with an elevated risk of mortality from MAFLD (66). Clinically, recent meta-analyses showed that the marine-based n-3 PUFAs significantly reduce alanine aminotransferase (ALT), aspartate aminotransferase (AST), and γ-glutamyl transferase (GGT) levels (67). Moreover, another meta-analysis demonstrated significant improvement in liver fat content after taking marine-based n-3 PUFAs (68). This benefit is also observed in younger populations. Another meta-analysis focusing on pediatric MAFLD showed that n-3 PUFA supplementation combined with health behavior adjustment had a positive effect on ALT, AST, and GGT levels (69). It was also suggested that dietary C20–22 n-3 PUFA supplementation may decrease MAFLD severity by reducing steatosis (70).

Currently, EPA alone or combined with DHA is considered a well-tolerated and effective agent for treating hypertriglyceridemia, and according to a recent advisory from the American Heart Association, prescription n-3 LCPUFAs at a dose of 4 g/day is recommended as a triglyceride-lowering option (13). The TG-lowering mechanism of DHA and EPA is multifactorial, involving the suppression of hepatic TG synthesis, inhibition of TG incorporation into VLDL particles, reduction of TG secretion, and promotion of TG clearance from VLDL, collectively leading to reduced plasma TG concentrations (71). Evidence from meta-analyses robustly supports this effect. Meta-analysis showed that n-3 PUFA supplementation lowered blood TG, but effects on HDL remain inconsistent (72). Similar promising effects of lowering TG and non-high-density lipoprotein cholesterol are shown in another recent meta-analysis of RCTs (12).

Maternal DHA and EPA supplementation exerts transgenerational effects on offspring during the fetal period. These transgenerational effects of maternal n-3 PUFA supplementation on fetal adipogenesis and thermogenesis have been investigated in animals only. Prenatal n-3 PUFA supplementation results in a decrease in fetal white fat accumulation, an accumulation of brown fat, and an increase in thermogenesis (15, 87). In contrast, a deficiency in maternal n-3 PUFAs affects the levels of growth hormone and fetal thermogenic-sensitive adipose tissue, as well as energy balance, in offspring, resulting in the body fat accumulation in offspring (88). Moreover, such a deficiency dysregulates differentiation during BAT development and downregulates uncoupling protein 1 (UCP1); since reduced expression of UCP1 reflects insufficient brown fat generation caused by an impairment of thermogenic fat development, this might lead to a higher risk of obesity later in life (88).

Furthermore, maternal n-3 PUFA supplementation promotes the development of brown fat production in the fetus and confers lasting thermogenic benefits to the offspring. Maternal n-3 PUFA supplementation reduced fetal white fat accumulation and promoted brown fat development. As for thermogenic potential, after the cessation of breastfeeding, both groups consumed an n-3 PUFA-free diet. At 11 weeks of age, exposure to cold increased the expression of UCP1 and PPARγ in the BAT and WAT of the fish oil group, increasing the rate of energy dissipation. Thus, maternal n-3 PUFA supplementation not only maintained stronger thermogenic potential in BAT but also was associated with increased adaptive thermogenesis in WAT, conferring sustained thermogenic advantages for offspring (15).

At the level of WAT-to-BAT conversion, maternal DHA and EPA upregulated genes that are associated with brown adipogenesis, as did that of thermogenic stimulators in the offspring. Notably, these changes occurred without changing the adipose tissue mass, suggesting a potential browning effect on WAT (87).

The results of animal and clinical studies related to how maternal DHA and EPA supplementation affects neonatal birth weight are inconsistent. On the one hand, prenatal DHA supplementation prolongs gestation and increases newborn body weight (77). DHA and EPA supplementation during pregnancy prolongs gestation and increases birth weight in offspring, and this increase may be safe and beneficial in reducing the risk of preterm birth and the risk of low birth weight (LBW) in infants (77, 83, 84, 86). Another study also revealed a reduced risk of preterm birth and an increase in birth weight (89). The rise in the birth weight of offspring following DHA and EPA supplementation during pregnancy may be related to a prolongation of gestation by affecting endogenous prostaglandin metabolism (86). N-3 LCPUFAs reduce the activity of the labor-promoting factors prostaglandin F2 alpha (PGF2α) and prostaglandin E2 (PGE2), which are important for uterine contractions and cervical ripening (90).

On the other hand, some animal studies have shown the offspring of maternal Wistar rats and Sprague–Dawley rats fed a HFD have lower birth weights (91, 92). As a decreased arachidonic acid (ARA) concentration is related to delayed development of offspring (93), a lower birth weight may be related to impaired endogenous synthesis of arachidonic acid (ARA) in the DHA/EPA-supplemented group via impaired Δ6-desaturase expression (92).

Finally, some studies have shown that prenatal marine-based n-3 PUFA supplementation does not affect the birth weight of offspring (81, 94–96). No effects on birth weight were observed in Wistar rat offspring (94, 95). Similar to a study in the clinical setting, this intervention does not affect birth weight, length, or head circumference (96). Similar consequences were reported by Foster et al. (81).

The mechanisms underlying the impacts of maternal DHA and EPA supplementation on transgenerational lipid metabolism involve multiple systems, like adipose tissue, the liver, the brain, and the gut (Figure 4). Research on maternal DHA and EPA supplementation-induced transgenerational changes in offspring WAT remains limited, and the fundamental mechanisms have been largely unexamined. For instance, studies indicate that a maternal EPA and DHA enriched diet reduces perirenal adipocyte size in offspring without affecting adipocyte number (87).

Unlike energy-storing WAT, BAT specializes in energy dissipation. In humans, the loss of active BAT depots contributes to the development of obesity (15). Importantly, EPA appears to be primarily responsible for the effects associated with adipocyte browning, whereas DHA has a negligible influence (109). Early stages of life are fundamental for fetal BAT development, with long-term consequences related to BAT function. Maternal n-3 PUFA intake stimulates fetal BAT development and upregulates uncoupling protein 1 (UCP1), PR domain-containing protein 16 (PRDM16), and GPR120 in the next generation (15). BAT induction of the expression of these brown-specific genes depends on the membrane receptor GPR120 that senses n-3 PUFAs. Fish oil intake upregulates both UCP1 and β3AR (110). Functionally, UCP1 serves as a key regulator during browning, while β-adrenergic receptor (β3AR) stimulation is vital for β-oxidation and lipolysis. DHA increases β-AR expression (111), which may actively affect its interaction with downstream adenylyl cyclase signaling, and this is vital for the recruitment of BAT (88). The activation of β3AR stimulates UCP1 expression through adenylyl cyclase signaling (112, 113). The plasma cAMP level is increased following maternal fish oil supplementation; cAMP is the downstream target of β3AR activation and regulates lipolysis and UCP-1-mediated thermogenesis (15). Thus, DHA and EPA may induce BAT recruitment and thermogenic responses through β3AR-UCP1 signaling. The offspring of maternal DHA- and EPA-supplemented mice exhibited upregulated expression of marker genes of beige and brown fat, both of which are related to energy expenditure (87). Such exposure also enhances thermogenic stimulators and potentially results in browning of WAT in offspring (87). Consequently, maternal n-3 PUFA supplementation may enable adipocytes within WAT to acquire BAT-like phenotypes, promoting energy dissipation through increased fatty acid oxidation in these depots (88).

Beyond direct gene regulation, maternal n-3 PUFA consumption enhances brown adipogenesis in offspring via epigenetic mechanisms that involve histone modifications and miRNA biogenesis (15). Placental transfer of n-3 PUFAs during pregnancy elevates its fetal levels, increasing cAMP concentrations and altering critical posttranslational modification (PTM) markers (H3K27Ac and H3K9me2) (15). This phenomenon accompanies epigenetic enzyme regulation, ultimately increasing the transcription of the BAT-specific genes PPARγ, UCP1, PRDM16, and peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α) (15). Concurrently, histone acetylation increases transcriptome-wide miRNA gene transcription and upregulates Drosha, which is an RNA double-stranded ribonuclease, thereby promoting nuclear pri-miRNA processing and mature miRNA generation (114). Through this coordinated regulation via histone modifications and miRNA networks, n-3 PUFA strengthens fetal BAT transcriptional programming, potentially mediating long-term metabolic benefits later in life (15).

Maternal supplementation with marine-based n-3 fatty acids alters hepatic lipid metabolism gene expression in the offspring. This protective effect of maternal DHA consumption on three-month-old offspring with MAFLD is linked to a decrease in the expression of hepatic mRNAs that encode proteins, including proteins that positively regulate lipogenesis and TG synthesis, the carbohydrate response element binding protein (ChREBP), fatty acid synthase (FASN), SCD, glycerol-3-phosphate acyltransferase, mitochondrial (GPAM), and diacylglycerol O-acyltransferase 2 (DGAT2) genes, as well as upregulation of genes supporting β-oxidation, such as PPAR-γ, CPT1a, peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), medium-chain acyl-CoA dehydrogenase (MCAD), and hydroxyacyl-Coenzyme A dehydrogenase (HADH) (16). It is widely accepted that the protective capacity of DHA consumption on the MAFLD development is primarily achieved through the combination of inhibition of lipogenesis and the promotion of β-oxidation; for example, the expression of lipogenesis-related SREBP-1c is downregulated, that of β-oxidation-related CPT I, ACO, and HMG-CoA synthase is upregulated, and that of lipolysis-related lipoprotein lipase (LPL) is upregulated in the livers of offspring following maternal fish oil intervention (92). Similarly, the expression of the lipogenic markers Srebf1c and Fasn is decreased in rats following maternal fish oil-supplemented HFD feeding (91, 95). The expression of thermogenesis-regulated and β-oxidation genes is substantially elevated in the livers of offspring whose mothers were fed EPA- and DHA-enriched diets for 21 days versus the normal dietary group, facilitating hepatic lipolysis (87). However, maternal DHA supplementation leads to decreased expression of β-oxidation-related genes in the liver. This may occur because, on the one hand, fatty acid oxidation-related genes are already expressed in patients with MAFLD, with conflicting results, and on the other hand, whether increased lipid oxidation in MAFLD has protective effects is unclear. This result may also be related to the low level of EPA that was used in this study, as studies point out that EPA is more potent than DHA in increasing mitochondrial fatty acid oxidation (16).

Beyond lipid metabolism genes, maternal DHA/EPA supplementation modulates other hepatic pathways. The children of mothers on a high-sugar diet exhibit a marked upregulation in the expression of Δ-9 Desaturase, while its expression is fully restored to the control level by DHA and EPA supplementation, suggesting a protective effect (115). Similarly, Δ6-desaturase expression has been found to decrease in the liver (92). On a separate note, hepatic betacellulin, which is a growth factor, is overexpressed in those whose mothers have metabolic syndrome, and betacellulin overexpression is weakened in offspring exposed to high maternal DHA intake (115, 116). Studies have identified the suppression of betacellulin as a key mechanism through which DHA exerts its therapeutic effects against inflammation and fibrosis in metabolic dysfunction-associated steatohepatitis (MASH), and then, the effect of transgenerational changes in betacellulin levels may be a mechanism of action for inhibiting the development of MASH in the offspring (115).

Finally, the endocannabinoid system (ECS), which is associated with lipid accumulation and positive energy metabolism (117) via CB1 activation (91), is implicated in obesity and MAFLD (118). Maternal fish oil supplementation has been observed to reduce ECS signaling, especially the protein content of CB1 (91). These findings collectively advance the DOHaD paradigm by demonstrating that hepatic metabolic programming during critical windows of development may significantly influence lifelong susceptibility to metabolic disorders.

The impacts of maternal DHA and EPA supplementation on appetite of the offspring, especially the effects on the hypothalamic region, are controversial. Early in life, leptin promotes the development of hypothalamic satiety-regulating pathways, and high/low leptin levels early in life may increase the risk of future obesity (119). Agouti-related peptide (AgRP) is generated by specific neurons in the hypothalamic arcuate nucleus (ARC). AgRP further promotes appetite, reduces energy expenditure, and increases obesity by antagonizing the effects of alpha-melanocortin-stimulating hormone (α-MSH) (120). Pro-opiomelanocortin (POMC) is another precursor polypeptide that is expressed in the ARC, and its processing products include α-MSH, which suppresses appetite and promotes energy expenditure (121).

Leptin, AgRP, and POMC collectively influence the structure of the hypothalamic pathway of energy homeostasis and regulate the balance between appetite promotion and appetite suppression (122). Notably, feeding mothers a prenatal high-n-3 PUFA diet directly upregulates AGRP and POMC, which are important hypothalamic neuropeptides that regulate appetite and satisfaction in female offspring and do not depend on leptin (119). This change, however, does not occur in male offspring. Maternal n-3 PUFA-supplemented male offspring with low birth weight and low circulating leptin levels may exacerbate catch-up growth during the vital time window of growth and development, leading to a greater likelihood of subsequent metabolic disorders (119). Thus, n-3 PUFA supplementation may transgenerationally affect neuropeptide dysregulation and reduce leptin, which is deleterious to the metabolic and developmental outcomes of the next generation (119).

Additionally, low maternal consumption of n-3 PUFAs induces overeating behavior in the offspring (123). For example, offspring of pregnant mice having an n-6-high and n-3-low diet exhibit upregulated dopamine release, thus increasing food consumption (123). Overall, the impacts of supplemental maternal DHA/EPA intake upon offspring are varied and complex, and the existence of a benefit still needs to be supported by additional research.

Maternal DHA and EPA may transgenerationally induce intestinal changes in the offspring, affecting gut microbiota structure, intestinal nutrient transport, morphological development, and barrier maintenance in early stages of life (17, 124). At birth, the gastrointestinal motility of newborns is immature, the activity of digestive enzymes is reduced, and the intestinal surface area for nutrient absorption is lower, preventing them from absorbing nutrients as effectively as adults (125). It is also important to distinguish between intestinal digestion (mechanical and enzymatic breakdown of foods), absorption (end products of digestion from the gastrointestinal tract into the blood and lymphatic vessels) and assimilation (effective physiological utilization), as the immature digestive tract of newborns may impose limitations on digestion and absorption, finally affecting the organism’s assimilation of nutrients (126, 127).

Maternal DHA and EPA supplementation promotes the upregulation of genes related to nutrient transport, thereby increasing nutrient transport capacity (17). N-3 LCPUFAs enhance nutrient absorption and assimilation, which aids in fulfilling the high nutritional demands for rapid growth and development in infants (125, 127). For instance, in weaning offspring from the maternal high-DHA group, genes related to carbohydrate transport sodium glucose co-transporter 1 (SGLT1) and glucose transporter 2 (GLUT2) were upregulated, potentially through the mTOR pathway, while lipid and protein transport genes were partly upregulated or downregulated (17). Nevertheless, proteomic and bioinformatic analyses of maternal high-DHA supplementation also demonstrated enhanced protein and fat absorption (17). In parallel, maternal DHA and EPA diets may improve the intestinal morphology of offspring, promote intestinal development, and may also protect the intestinal barrier by maintaining intestinal epithelial integrity and stimulating the expression of key genes and tissue morphology biomarkers to promote early intestinal health in offspring, thereby inhibiting the intergenerational passage of metabolic diseases (124). As the primary site of nutrient absorption, the morphology of the small intestine is crucial for providing adequate nutrition for growth and development (128). Villus height, surface, and the villus height-to-crypt depth (V/C) ratio are associated with nutrient transport, elevated in offspring subjected to a high-DHA maternal diet, indicating that supplementing the maternal diet with DHA during lactation improves intestinal nutrient transport in offspring under basal conditions (17). Though the actual assimilation and systemic utilization of these nutrients may increase as intestinal transportation increases, the overall efficiency of nutrient utilization remains lower than in mature individuals. This reflects the limitations imposed by the immature gastrointestinal tract in infants, despite an absolute increase in nutrient absorption.

In addition, research has indicated that maternal high-DHA intake leads to a downward trend in the Firmicutes/Bacteroidetes ratio in offspring, which is a microbiota marker associated with obesity (17); There are increased abundances of beneficial microbiota such as Ruminococcus, which is related to SCFAs production. Lactobacillus is associated with improving the intestinal barrier (17, 129). Barnesiella is associated with taurine-conjugated bile acids (17, 130). There are lower abundances of harmful or obesity-associated bacteria such as Desulfovibrio, Alistipes, Acetatifactor, Oscillibacter, Harryflintia, Intestinimonas, and Pseudoflavonifractor (17). These changes lead to significantly enhanced carbohydrate, fat, and protein digestion and absorption, as well as improved systemic metabolism, which benefits early growth and development (17). This demonstrates that maternal n-3 PUFA supplementation during pregnancy or breastfeeding may increase the abundance of metabolically beneficial microbiota while reducing the abundance of harmful or obesity-associated bacteria, and these changes in the microbiota may enhance systemic metabolism and promote early growth and development (17).

Finally, chronic low-grade inflammatory processes that drive obesity phenotypes allow for their perinatal transfer from mothers to their infants, which seems to be gut-initiated through the disruption of the intestinal barrier (131). Evidence indicates that maternal DHA and EPA intake may promote the expression of key genes and tissue morphology biomarkers to promote early intestinal health in offspring (124). A menhaden fish oil supplemented diet increases crypt length and goblet cell counts to increase mucus secretion (124). It also regulates ileal and proximal colon morphology, and upregulates the expression of antimicrobial proteins regenerating family member gamma (REG3γ), mediators like resistin-like molecule β (Relmβ), and zonula occludens (ZO-1), which play key roles in promoting mucosal barrier integrity, thereby helping to maintain mucosal integrity (124). Therefore, maternal DHA and EPA intake may protect the intestinal barrier in offspring during early life stages through intestinal immune regulation and inhibit the transgenerational transmission of metabolic inflammation (124, 131).

After birth, offspring may obtain DHA and EPA through breastfeeding or formula feeding. To guide intake, the Food and Agriculture Organization (FAO) of the United Nations and the World Health Organization (WHO) proposed that the average prenatal and lactation nutrient requirement for DHA should be 200 mg/day and that the combined intake of DHA and EPA should be 300 mg/day (132). During gestation, when the RBC DHA level is below 5%, a daily intake of at least 600–800 mg DHA is advised (75). For 0–6 months-old infants, the recommended intake of DHA is 0.1–0.18% of overall energy intake, that is, about 40–130 mg/day (132).

In the case of formula feeding, it is also significant to focus on the levels of DHA and EPA in infant formula, and these levels should be similar to those in human milk. Current Chinese regulations stipulate that infant formula must contain at least 15 mg of DHA per 100 kcal, whereas the European Union regulations indicate a fundamental requirement of ≥20 mg of DHA per 100 kcal (133).

Beyond direct supplementation, maternal diet is a modifiable and vital factor during the periconceptional period (134). Specific dietary patterns enriched with DHA and EPA during pregnancy represent promising nutritional interventions, with benefits observed for both maternal and metabolism in the offspring (135).

For instance, maternal adherence to a Mediterranean diet, characterized by moderate poultry and fish consumption, has been linked to reduced childhood abdominal obesity and improved neonatal metabolic profiles, including favorable lipoprotein levels, homocysteine concentrations, and insulin sensitivity (135). Similarly, the New Nordic Diet, which emphasizes fruits, vegetables, rapeseed oil, and fatty fish, is abundant in DHA and EPA (136). Likewise, the Okinawan diet in coastal populations ensures high n-3 LCPUFA intake (119), providing a natural model of n-3 PUFA enrichment (137). Notably, both the Okinawan diet and the New Nordic Diet have demonstrated efficacy in improving weight management and lipid homeostasis in patients with type 2 diabetes, underscoring their broader metabolic benefits (138).

Despite these promising findings, research on the transgenerational metabolic effects of these diets remains limited. Therefore, future research should examine how those dietary patterns affect lipid metabolism and metabolic health in offspring in the long run.