High-fat diet, gut dysbiosis, and oxidative stress: A synergistic triangle in metabolic dysfunction-associated steatotic liver disease pathogenesis

Abstract

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a prominent metabolic disease characterized by hepatic steatosis, inflammation, and progressive liver damage, in which oxidative stress plays a crucial pathogenic role. Increasing attention has been drawn to the contributions of a high fat diet (HFD) and gut dysbiosis in the onset and progression of MASLD. These factors compromise intestinal barrier integrity, promote endotoxemia, induce lipid peroxidation, and activate pro-inflammatory signaling pathways, contributing to oxidative stress. Excessive production of reactive oxygen species disrupts hepatic redox homeostasis, impairs mitochondrial function, and amplifies inflammatory responses, thereby accelerating hepatic fibrosis and disease progression. This review highlights the triangular and synergistic relationship among HFD, gut dysbiosis, and oxidative stress in MASLD pathogenesis. It provides a comprehensive overview of antioxidant interventions, including lifestyle modifications, dietary antioxidants, natural bioactive compounds, and pharmacological agents, aiming at providing promising MASLD management in future clinical applications.

Key Words: Metabolic dysfunction-associated steatotic liver disease; High-fat diet; Gut dysbiosis; Oxidative stress; Intestinal barrier dysfunction

Core Tip: This review proposes a unifying framework in which a high-fat diet, gut dysbiosis, and oxidative stress form a self-reinforcing pathogenic triad driving metabolic dysfunction-associated steatotic liver disease. We synthesize evidence showing how diet-induced microbial imbalance disrupts intestinal barrier integrity, promotes endotoxemia, and amplifies hepatic oxidative stress, mitochondrial dysfunction, inflammation, and fibrosis. By positioning oxidative stress as a central mechanistic nexus linking diet and microbiota, this review highlights antioxidant-based lifestyle, nutritional, and pharmacological strategies as promising, integrative approaches for prevention and treatment.

INTRODUCTION

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as nonalcoholic fatty liver disease (NAFLD), is characterized by hepatic steatosis involving more than 5% of hepatocytes in the absence of significant alcohol consumption or other identifiable causes of hepatic fat accumulation. MASLD is further categorized into simple steatosis, which lacks hepatocellular injury, and metabolic dysfunction-associated steatohepatitis (MASH), a more severe phenotype characterized by lobular inflammation and hepatocyte ballooning, that drives fibrosis progression[1]. MASLD has emerged as the most prevalent chronic liver disease worldwide, affecting approximately 38% of adults and 7%-14% of children and adolescents[2]. With the rising incidence of obesity, sedentary lifestyles, and aging populations, the global burden of MASLD continues to escalate[3]. Despite its high prevalence, few drugs have been approved for its treatment. Therefore, a thorough understanding of the disease’s underlying mechanisms is essential for developing effective interventions and preventive strategies.

A high-fat diet (HFD) is an energy-dense dietary pattern that contributes to insulin resistance (IR), obesity, diabetes, and other metabolic disorders, particularly MASLD[4]. The primary pathogenic feature of MASLD is excessive lipid accumulation in the liver, which serves as a central organ regulating systemic lipid metabolism. Following ingestion, dietary fats are metabolized into triglycerides and assembled into chylomicrons in the intestine. While surrounding tissues such as muscle and adipose tissue can utilize or store the free fatty acids (FFAs), excessive lipid intake leads to elevated FFA levels in the portal circulation and subsequent hepatic accumulation[5]. This lipid overload renders the liver especially vulnerable to diet-induced steatosis and injury.

The gut microbiota comprises a highly complex and diverse community of microorganisms that play a crucial role in maintaining host metabolic homeostasis and other physiological functions[6]. However, this microbial balance can be disrupted by various factors, leading to dysbiosis, typically characterized by a collapse in microbial diversity and alterations in microbial composition[7]. Evidence suggests that patients with MASLD exhibit a distinct gut microbiota profile compared to healthy individuals, including shifts in the abundance of specific microbial genera[8]. This microbial imbalance is increasingly recognized as a contributor to MASLD pathogenesis and progression through mechanisms such as increased intestinal permeability, systemic inflammation, and altered metabolite production[9].

Oxidative stress (OxS) arises from a disrupted balance between oxidants and antioxidants[10]. Reactive oxygen species (ROS), which include free radicals (e.g., superoxide anion and hydroxyl radical) and non-radical species [e.g., hydrogen peroxide (H₂O₂)], can damage cellular structures if not adequately neutralized[11,12]. The body relies on enzymatic and non-enzymatic antioxidant systems to detoxify ROS and prevent cellular damage[13,14]. Importantly, OxS activates redox-sensitive signaling pathways such as the nuclear factor erythroid 2-related factor 2 (Nrf2), which regulates genes involved in antioxidant defense and detoxification[15]. Under physiological conditions, ROS serve as signaling molecules in various metabolic processes, immune responses, and cell proliferation[11]. However, excessive ROS under OxS conditions lead to pathological modifications of lipids, proteins, and nucleic acids, contributing to cellular damage and the development of diseases including MASLD.

The pathogenesis of MASLD involves both genetic and environmental factors and remains incompletely understood[16]. The earlier “two-hit” hypothesis proposed that hepatic fat accumulation (first hit) sensitizes the liver to OxS and inflammation (second hit)[17,18]. Although this model provided useful insights, it failed to capture the multifactorial complexity of MASLD. A more comprehensive “multiple parallel hits” hypothesis has since emerged, suggesting that MASLD results from the convergence of multiple simultaneous insults, including lipid metabolism disorders, lipotoxicity, OxS, mitochondrial and endoplasmic reticulum (ER) dysfunction, endotoxemia, cytokine alterations, and genetic predisposition[10,19]. Elucidating the interplay among these factors is critical to developing integrative strategies for MASLD prevention and management.

Although HFD, gut dysbiosis, and OxS have each been independently implicated in MASLD, a comprehensive understanding of their interconnections remains lacking. This narrative review synthesizes current evidence to elucidate the triangular and synergistic interactions among these factors in MASLD pathogenesis and to highlight antioxidant-based therapeutic strategies.

METHODOLOGY

We performed a targeted literature search using PubMed/MEDLINE and Google Scholar. The search strategy combined Medical Subject Headings terms and free-text keywords, including but not limited to “MASLD”, “metabolic dysfunction-associated steatotic liver disease”, “NAFLD”, “NASH”, “high-fat diet”, “gut microbiota”, “microbiome”, “gut dysbiosis”, “oxidative stress”, “reactive oxygen species”, “lipotoxicity”, and “inflammation”. Duplicate records were removed prior to screening. Reference lists of these articles were subsequently reviewed, resulting in a total of 194 sources included in this narrative review.

HFD AND HEPATIC LIPID METABOLISM

Hepatic fatty acid uptake plays a central role in maintaining triglyceride homeostasis within the liver. Hepatic lipid homeostasis is maintained through the dynamic balance between lipid input, including dietary fatty acids, de novo lipogenesis (DNL), and intracellular lipid stores, and lipid output, such as mitochondrial β-oxidation and export via lipoproteins. Fat accumulation in hepatocytes occurs when lipid influx exceeds efflux[4].

The liver is particularly susceptible to diet-triggered steatosis due to its direct exposure to dietary lipids and carbohydrates via the portal vein. DNL is upregulated in response to elevated carbohydrate and insulin levels, which stimulate key lipogenic transcription factors, including carbohydrate-responsive element-binding protein (ChREBP) and sterol regulatory element-binding protein 1c (SREBP-1c), both of which are involved in gluconeogenesis and lipogenesis[20]. Mitochondrial β-oxidation is the primary pathway for lipid catabolism. While short- and medium-chain fatty acids freely diffuse into mitochondria, long-chain fatty acids require transport by carnitine palmitoyl transferase-1 (CPT-1)[16]. However, HFD significantly suppress CPT-1 messenger RNA expression, impairing fatty acid oxidation[21]. IR further disrupts DNL, adipose tissue lipolysis, and fatty acid export[20]. Collectively, when hepatic lipid accumulation overwhelms physiological regulation, it triggers a cascade of metabolic disturbances that promote the development of MASLD.

Specific dietary components play critical roles in the progression of MASLD. Diets high in fructose is also recognized as a potent driver of MASLD. Fructose metabolism strongly increases protein levels of all DNL enzymes and upregulates lipogenic transcription factors, specifically ChREBP and SREBP-1c, promoting the accumulation of intrahepatic triglycerides[22] and inhibiting fatty acid β-oxidation[23]. As the most abundant dietary antioxidants, polyphenols exert hepatoprotective effects in part via activation of adenosine 5’-monophosphate-activated protein kinase (AMPK) and Nrf2 signaling[24]. A diet deficient in polyphenols promotes the release of pro-inflammatory cytokines and exacerbating liver injury.

Saturated fatty acids (SFAs) and unsaturated fatty acids (UFAs) represent the two major classes of dietary fatty acids. SFAs have been consistently associated with IR, hepatic lipid accumulation, and pro-inflammatory responses[25]. Accumulating evidence suggests that SFAs may activate Toll-like receptor (TLR) 4[26,27], potentially due to their structural similarity to lipopolysaccharide (LPS)[28]. Trans fatty acids (TFAs) are a subclass of UFAs characterized by one or more unconjugated double bonds in the trans configuration. Most TFAs originate from industrial processing [industrial TFAs (iTFAs)], whereas a smaller proportion arises from natural fermentation in the rumen of ruminant animals [ruminant TFAs (rTFAs)][29]. However, limited preclinical evidence indicates that iTFAs, but not rTFAs, adversely affect insulin sensitivity and lipid metabolism and may promote inflammation and stress[30]. The differential biological effects of rTFAs appear to be mediated by distinct signaling pathways, such as activation of peroxisome proliferator-activated receptor-α (PPARα), and warrant further investigation[31].

GUT DYSBIOSIS AND MICROBIAL METABOLITES

The gut microbiota is intricately involved in the pathogenesis and progression of MASLD. The interplay between microbial metabolites, immune activation, and endotoxemia, primarily due to intestinal barrier dysfunction, synergistically drives inflammation and OxS in MASLD[9,32].

Gut microbes employ diverse enzymatic systems to produce a wide array of metabolites that influence host metabolism[33]. Among these, short-chain fatty acids (SCFAs) are particularly significant, serving as vital energy sources for colonocytes and playing essential roles in metabolic and immune regulation[34]. For example, butyric acid supports intestinal barrier integrity and inhibits lipogenic transcription factors such as ChREBP and SREBP-1c[35], while propionic acid may exacerbate MASLD by promoting adipogenesis and gluconeogenesis[36]. SCFAs also activate G protein-coupled receptors in the gut and adipose tissues, slowing intestinal motility and enhancing nutrient absorption, which may further contribute to MASLD progression[37].

Bile acids (BAs), the principal constituents of bile, consist of primary BAs (PBAs) synthesized in the liver and secondary BAs (SBAs) produced by gut microbial conversion. PBAs regulate microbial composition by directly suppressing pathogenic bacteria and by activating the intestinal farnesoid X receptor (FXR)[38]. FXR activation enhances glycogen synthesis and inhibits SREBP-1c expression, thereby reducing hepatic fat accumulation[39]. Conversely, a reduction in SBAs impairs FXR signaling, while excessive SBAs may induce DNA damage and ROS generation. Changes in gut microbiota and liver function can further alter BA profiles and their metabolic effects.

Choline metabolism is also closely linked to hepatic lipid regulation. Choline deficiency impairs the synthesis and secretion of very low-density lipoproteins in hepatocytes, leading to hepatic lipid accumulation[40,41]. Choline-derived metabolites such as trimethylamine-N-oxide have been implicated in hepatic inflammation and injury[42]. Other microbial byproducts, including ethanol, acetaldehyde, phenols, ammonia, and related compounds, can also contribute to hepatic inflammation and OxS.

OXS: CENTRAL MECHANISM IN MASLD

OxS driven by ROS production and chronic inflammation, is now recognized as a central mechanism in the onset and progression of MASLD. A close interplay exists between OxS and mitochondrial dysfunction, as mitochondria are the primary source of intracellular ROS[13,43]. Studies have reported various mitochondrial abnormalities in MASLD, including ultrastructural damage, altered morphology, mitochondrial DNA (mtDNA) mutations and depletion[44], reduced electron transport chain (ETC) activity, and impaired β-oxidation. Lipid metabolic imbalance contributes significantly to mitochondrial impairment. One major fate of hepatic lipids is mitochondrial β-oxidation, which generates energy via the ETC[45]. In MASLD, excessive FFAs overload already compromised mitochondria[46]. The excessive oxidative load and elevated electron flux within the ETC lead to incomplete electron transfer, resulting in electron leakage and increased ROS generation[43,47]. Moreover, FFAs and ROS compromise mitochondrial function by altering inner membrane permeability and inhibiting key components of the ETC, including complexes I and II and adenosine triphosphate (ATP) synthase. Superoxide and H₂O₂, produced in the mitochondrial inner membrane, interact readily with nearby mtDNA, causing point mutations and deletions.

The ER is another key intracellular source of ROS. ER stress, marked by disruption of protein-folding homeostasis, plays a pivotal role in MASLD pathogenesis. The ER supports proper folding and assembly of nascent proteins, a process that inherently generates ROS through disulfide bond formation[48]. Under stress conditions, such as lipid overload or the accumulation of misfolded proteins, the unfolded protein response (UPR) is activated to restore homeostasis[49]. UPR initiates the expression of ATP-dependent chaperone proteins to refold misfolded proteins, thereby increasing energy demands on already dysfunctional mitochondria. The UPR is mediated by three key transmembrane sensors (PERK, IRE1, and ATF6), which regulate genes involved in antioxidant defense and inflammatory signaling. Prolonged ER stress enhances ROS production by activating pro-apoptotic pathways such as CHOP (regulated by PERK and ATF6), c-Jun N-terminal kinase (via IRE1), and nuclear factor-κB (NF-κB) (via ATF6). Furthermore, PERK-mediated inhibition of Nrf2 impairs antioxidant responses[50-53]. ER stress also disrupts calcium homeostasis, exacerbating mitochondrial dysfunction[54]. Together, these mechanisms lead to ROS-mediated cell damage and apoptosis.

Numerous studies report reduced antioxidant defenses in individuals with MASLD, including decreased levels of superoxide dismutase (SOD), catalase, and glutathione (GSH)[55]. These reductions impair enzymatic detoxification of ROS, intensifying OxS and contributing to hepatic damage and MASLD progression.

INTERACTIONS AMONG DIET, MICROBIOTA AND OXS

Dietary composition profoundly influences the structure and diversity of the gut microbiota. Polyphenol-rich diets have been shown to specifically restore the abundance of beneficial gut microbes such as Lactobacillus and Bifidobacterium, while inhibiting potentially harmful bacteria[56]. In contrast, the Western diet, rich in fats and fructose, reshapes microbial communities by altering nutrient availability and the intestinal environment, promoting the expansion of lipid-adapted bacteria while depleting beneficial species[57,58]. Animal studies indicate that HFD increases the relative abundance of Firmicutes, Escherichia, and Shigella, while reducing Bacteroidetes, Lactobacillus, and Bifidobacterium[59,60]. HFD is also associated with enrichment of LPS-producing bacteria[61] and taurine-metabolizing bacteria[62], thereby altering inflammation and BAs metabolism.

Beyond its effects on microbial composition, a HFD directly impairs intestinal barrier function and increases intestinal permeability[63]. The intestinal barrier, composed of epithelial cells joined by tight junctions and covered by a mucus layer, prevents luminal microbiota from entering host circulation[64]. Studies suggest that HFD compromises this barrier via several mechanisms: (1) Downregulation or aberrant expression of tight junction proteins and abnormal mucus secretion[65]; (2) Chylomicron accumulation between epithelial cells, increasing mechanical stress that disrupts tight junctions or perforates the basal membrane[66,67]; and (3) Activation of mast cells during fat absorption, releasing mediators such as histamine and prostaglandin D2 that are associated with increased intestinal permeability[68]. These disruptions promote the translocation of luminal antigens, leading to enterocyte OxS and apoptosis, and contributing to the “leaky gut” phenotype.

Gut dysbiosis further exacerbates intestinal barrier dysfunction, creating a self-reinforcing pathogenic cycle. The gastrointestinal tract harbors a range of immune cells within gut-associated lymphoid tissue, and disturbances in microbial composition can impair immune regulation and elicit inflammatory responses[69]. Chronic inflammation, mediated by immune cells and cytokines, disrupts tight junctions, injures epithelial cells, and alters the composition of the mucus layer[70-72]. The overgrowth of pathogenic microbes further compromises the protective roles of beneficial bacteria in maintaining barrier integrity[73]. As a result, increased intestinal permeability, or “leaky gut”, permits the translocation of microbial components, toxins, and metabolites into systemic circulation[74,75]. Among these microbial products, LPS, a key structural component of gram-negative bacterial cell walls, plays a pivotal role in triggering endotoxemia[61]. Once in the bloodstream, LPS activates immune cells expressing TLR4, initiating chronic hepatic inflammation[76]. Kupffer cells, which express high levels of TLR4 in the liver, are central mediators of this response, producing cytokines, chemokines, and ROS[77,78]. The LPS-TLR4 interaction activates downstream signaling cascades, including NF-κB, leading to the secretion of pro-inflammatory cytokines[79,80]. This process further damages intestinal barrier function and perpetuates MASLD progression. Tumor necrosis factor-alpha (TNF-α), a major cytokine induced by LPS-TLR4 signaling, plays a critical role in hepatotoxicity, inflammation, and IR[81]. These inflammatory and oxidative pathways form a vicious cycle that exacerbates hepatic injury, promotes gut barrier dysfunction, and sustains gut dysbiosis.

Within the liver, chronic exposure to excess FFAs, inflammatory mediators, and OxS promotes lipid overload and facilitates the accumulation of toxic lipid intermediates, including ceramides and diacylglycerols (DAGs)[16,19]. Reduced oxidative capacity further contributes to intracellular triglyceride accumulation, which is highly susceptible to ROS-induced lipid peroxidation. Lipotoxic byproducts such as malondialdehyde (MDA) and 4-hydroxy-2-nonenal (4-HNE) further exacerbate oxidative injury[82]. These lipid intermediates cause extensive damage to cellular and subcellular structures, disrupt macromolecular integrity, and impair organelle function[83]. Ceramides inhibit mitochondrial β-oxidation and enhance intramitochondrial ROS generation[84], whereas DAGs and ceramides activate pro-inflammatory and pro-apoptotic signaling pathways, including NF-κB and c-Jun N-terminal kinase[85]. In parallel, MDA and 4-HNE inhibit cytochrome c oxidase, uncouple ETC complex II, destabilize mitochondrial membranes, and induce mtDNA mutations[86]. Subsequent leakage of damaged mtDNA into the cytosol activates innate immune receptors and downstream inflammatory cascades[87]. These mitochondrial abnormalities impair β-oxidation, enhance pro-inflammatory cytokine production, exacerbate hepatocellular triglyceride accumulation, and diminish ROS clearance, thereby establishing a self-amplifying cycle of OxS and mitochondrial dysfunction that accelerates liver injury, inflammation, fibrosis, and disease progression (Figure 1).

Figure 1 Interconnected roles of high-fat diet, gut dysbiosis, and oxidative stress in the pathogenesis of metabolic dysfunction-associated steatotic liver disease. The diagram illustrates how a high-fat diet induces gut microbiota imbalance and promotes oxidative stress, while gut dysbiosis further compromises intestinal barrier function and triggers systemic inflammation. These interacting pathways collectively drive hepatic lipid accumulation, oxidative injury, and disease progression. MASLD: Metabolic dysfunction-associated steatotic liver disease.

ANTIOXIDANT-BASED TREATMENT STRATEGIES

Current management strategies for MASLD primarily involve lifestyle modifications, antioxidant interventions, and combination therapies. Among these, antioxidants, including dietary supplements, natural bioactive compounds, and pharmacological agents, have shown promising potential in mitigating MASLD by targeting OxS and restoring redox homeostasis. In this section, we provide a comprehensive overview of antioxidant-based therapeutic approaches and their underlying mechanisms in the context of MASLD (Figure 2).

Figure 2 Antioxidant-based management strategies for metabolic dysfunction-associated steatotic liver disease. The diagram illustrates promising antioxidant-based treatment for metabolic dysfunction-associated steatotic liver disease (MASLD), including lifestyle modifications (exercise and therapeutic diets), dietary and natural bioactive antioxidants, and pharmacological agents. They ameliorate MASLD mainly through normalizing lipid metabolism, modulating gut microbiota and barrier integrity, and attenuating inflammation and reactive oxygen species. GLP-1RAs: Glucagon-like peptide-1 receptor agonists; SGLT-2i: Sodium-glucose cotransporter-2 inhibitors; MD: Mediterranean diet; VitE: Vitamin E; VitC: Vitamin C; ROS: Reactive oxygen species.

Lifestyle modifications

Lifestyle interventions, including exercise and dietary changes, remain the cornerstone of MASLD management.

Exercise: Exercise is widely recognized as a cost-effective, non-pharmacological intervention with both therapeutic and preventive benefits in metabolic diseases such as MASLD[88,89]. In addition to improving liver health, regular physical activity mitigates key risk factors for cardiovascular disease and hypertension[90]. Substantial clinical evidence supports the effectiveness of various forms of exercise, including both resistance and aerobic training. For instance, 12 weeks of high-intensity interval training or aerobic exercise has been shown to reduce serum triglyceride levels, liver enzyme activity, and biomarkers of inflammation and OxS[91,92]. Similarly, a 12-week resistance training regimen involving push-ups and squats was associated with delayed MASLD progression[93]. Current guidelines recommend that patients with MASLD engage in at least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity physical activity per week[94].

The hepatoprotective effects of exercise in MASLD are mediated through several mechanisms, including enhanced mitochondrial β-oxidation of fatty acids, suppression of lipogenesis, and reduction of intrahepatic fat accumulation[95,96]. Exercise also stimulates the activity of endogenous antioxidant enzymes and reduces OxS, inflammation, and mitochondria-mediated apoptosis[97,98]. Studies have shown that exercise activates mitogen-activated protein kinase, which in turn induces the NF-κB signaling pathway, leading to upregulation of antioxidant defense enzymes[99-101]. Moreover, exercise in combination with cold exposure has been reported to suppress the transforming growth factor-β/SMAD2 signaling pathway and activate the fibroblast growth factor (FGF) 21-β-klotho/FGF receptor 1 axis, thereby improving lipid metabolism and attenuating hepatic fibrosis and injury in MASLD models[102,103].

Therapeutic dietary patterns: A meta-analysis reported that adherence to Western dietary patterns is associated with a 56% increased risk of MASLD, underscoring the critical role of dietary habits in disease development and progression[104]. Dietary interventions that reduce carbohydrate and free sugar intake, and consequently restrict total caloric intake, have demonstrated hepatoprotective effects, making them a promising strategy for MASLD management[105]. Among these, caloric restriction remains the most widely adopted dietary approach.

Compared to diets high in saturated fats and sucrose but low in dietary fiber, the Mediterranean diet (MD), characterized by high consumption of fruits, vegetables, fish, whole grains, nuts, seeds, and olive oil, has demonstrated superior health benefits[106]. The European Association for the Study of the Liver-European Association for the Study of Diabetes-European Association for the Study of Obesity Clinical Practice Guidelines strongly recommend MD as a therapeutic option for MASLD[1]. Clinical studies have shown that MD reduces hepatic steatosis and fibrosis, alleviates IR and hyperlipidemia, promotes weight loss[107-109], and provides cardiovascular protection, thereby improving overall clinical outcomes in MASLD. Intervention studies have reported significant reductions in body weight, blood pressure, and cardiometabolic risk factors following MD adoption. Similarly, clinical trials in adolescents with obesity and MASLD have shown that 12 weeks of MD intake leads to improvements in body mass index, fat mass, hepatic steatosis, inflammatory and OxS markers, as well as reductions in serum transaminase levels[110-112].

The MD is a rich source of polyphenols and UFAs. Polyphenols are widely distributed in fruits, tea, berries, coffee, red wine, and dark chocolate and can be broadly classified into flavonoids (e.g., flavones, anthocyanins) and non-flavonoid compounds (e.g., phenolic acids, hydroxycinnamic acids, lignans, and tannins)[113]. Accumulating evidence indicates that polyphenols attenuate OxS, enhance fatty acid β-oxidation, improve IR, modulate DNL, and influence gut microbiota composition[24]. The therapeutic potential of representative flavonoids, including resveratrol, quercetin, and curcumin, in MASLD will be discussed in subsequent sections.

UFAs are structurally classified into polyunsaturated fatty acids (PUFAs) and monounsaturated fatty acids (MUFAs). The two principal PUFA families are the n-3 and n-6 classes. n-3 PUFAs, predominantly derived from marine and plant sources, exert hepatoprotective effects. Mechanistically, n-3 PUFAs alleviate hepatic steatosis by suppressing DNL while concomitantly activating PPARs to enhance fatty acid oxidation[114]. In contrast, the role of n-6 PUFAs, which are abundant in vegetable oils, is more complex, as an excessively high dietary n-6/n-3 ratio has been associated with a pro-inflammatory milieu[115,116]. MUFAs, primarily obtained from olive oil, avocados, and nuts, constitute a cornerstone of the MD. MUFAs intake has been consistently associated with improved insulin sensitivity and marked reductions in hepatic fat content[117].

In addition to MD, several emerging dietary strategies are being investigated for MASLD management. The ketogenic diet (KD), characterized by extremely low carbohydrate and protein intake but high fat content[118], has garnered attention for its effects on liver mitochondrial metabolism and redox balance[119]. However, potential cardiovascular and renal complications associated with KD, as reported in animal and clinical studies, remain a concern[120,121]. The long-term sustainability and safety of KD in individuals with MASLD require further investigation. Low-fat diets have also been shown to improve hepatic steatosis, liver enzymes, and IR in both adult and pediatric MASLD populations[122], although their benefits appear comparable or slightly inferior to those of MD. High-protein diets, whether animal- or plant-based, have demonstrated effectiveness in reducing hepatic fat accumulation, IR, and systemic inflammation[123]. Nonetheless, further long-term, controlled studies are needed to evaluate the safety, efficacy, and sustainability of these dietary interventions in MASLD.

Dietary antioxidant supplements

Vitamin C (VitC) and vitamin E (VitE) are classical antioxidants known to attenuate OxS by scavenging ROS. Several studies have reported beneficial effects of VitE and VitC supplementation in patients with MASLD[124-126].

VitE, a lipid-soluble vitamin primarily stored in the liver and adipose tissue, exerts antioxidant effects through multiple mechanisms. Experimental evidence suggests that the protective actions of VitE and its homologues may be attributed to the suppression of OxS and inflammation, inhibition of hepatic DNL, activation of the Nrf2 signaling pathway, protection against cellular injury, and normalization of lipid metabolism[127-130]. The PIVENS trial demonstrated that VitE supplementation (800 IU/day) significantly improved the NAFLD activity score, liver enzyme levels, steatosis, lobular inflammation, and hepatocellular ballooning although it did not improve fibrosis when compared to pioglitazone or placebo groups[131]. Additional clinical studies have confirmed that VitE therapy reduces intrahepatic lipid accumulation, slows MASLD progression, and improves liver histology[132-134]. Importantly, large-scale prevention trials, such as the SELECT study, have demonstrated a significant increase in prostate cancer risk associated with high-dose VitE supplementation, underscoring important safety concerns regarding its therapeutic use[135].

VitC, an essential water-soluble vitamin obtained exclusively through the diet, has shown variable therapeutic effects in MASLD. Some studies suggest that VitC supplementation exerts hepatoprotective effects, including improvements in liver histology and reductions in serum transaminase levels[136,137]. The beneficial actions of VitC may involve modulation of gut microbiota and BA metabolism[138], as well as attenuation of inflammation and apoptosis, potentially mediated by upregulation of PPARα and genes involved in β-oxidation[139,140].

Natural bioactive compounds

Accumulating evidence from preclinical models has highlighted the therapeutic potential of natural bioactive compounds in the treatment of liver diseases, including MASLD[141,142]. However, results from human studies remain inconsistent, likely owing to rapid metabolism, limited systemic bioavailability, small sample sizes, heterogeneous patient populations, and variability in treatment duration. Consequently, high-dose supplementation of natural bioactive compounds remains controversial, and well-designed, large-scale clinical trials are required to validate their efficacy and elucidate the underlying mechanisms.

Quercetin (3,3’,4’,5,6-pentahydroxyflavone), a widely distributed dietary flavonoid found in fruits and vegetables, exhibits strong antioxidant and anti-inflammatory properties[143]. Preclinical studies suggest that quercetin ameliorates MASLD by attenuating endotoxemia (via TLR4/NF-κB)[144], reducing inflammation (via TNF-α)[145], restoring redox homeostasis[146-148], and modulating lipid metabolism (via regulation of DNL and β-oxidation)[149]. Although a randomized, double-blind, placebo-controlled crossover trial demonstrated that 12 weeks of quercetin supplementation significantly reduced intrahepatic lipid content[150], some animal studies revolved possible critical safety aspects involving oral quercetin application like nephrotoxicity and tumor promotion[151].

Resveratrol (3,5,4’-trihydroxystilbene), a natural polyphenol present in grapes, berries, peanuts, and red wine, has been widely studied for its therapeutic potential in metabolic disorders[152]. In animal models of MASLD, resveratrol improved glucose and lipid metabolism, suppressed inflammation, and reduced OxS[153,154]. These effects are thought to be mediated through activation of Nrf2, silent information regulator 1 (SIRT1), and protein kinase A/AMPK/PPARα pathways[155-157]. Resveratrol has also been shown to promote mitochondrial biogenesis and enhance expression of mitochondrial respiratory chain proteins[158]. While some clinical trials in MASLD patients have reported reductions in hepatic steatosis, liver enzymes, and inflammatory markers[159,160], other studies have failed to confirm consistent therapeutic benefit[161-163].

Curcumin, a polyphenolic compound extracted from the rhizome of Curcuma longa, is well known for its potent antioxidant, anti-inflammatory, and hepatoprotective properties[164,165]. Both preclinical and clinical studies have reported that curcumin significantly improves hepatic lipid accumulation, oxidative damage, inflammation, and fibrogenesis by modulating antioxidant enzyme activity (e.g., SOD, PPARs), and regulating immune cell infiltration[166].

Silybin, the primary bioactive constituent of silymarin extracted from Silybum marianum[167], possesses antioxidant, anti-fibrotic, and anti-inflammatory effects[168]. Recent preclinical and clinical studies have demonstrated that silybin can improve hyperlipidemia, hepatic fibrosis, and inflammation in models of MASH, primarily through activation of key signaling pathways, such as SIRT1/AMPK, nicotinamide adenine dinucleotide/SIRT2, and NF-κB[169-172].

Pharmaceutical agents

Glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1RAs), initially developed for the treatment of type 2 diabetes mellitus (T2DM), have also demonstrated considerable promise in MASLD[173]. Agents such as liraglutide and semaglutide have been shown to reduce hepatic steatosis and IR, in part through enhanced β-oxidation, and to promote histological resolution of steatohepatitis in patients with MASLD[174,175]. GLP-1 receptors are expressed on immune cells, indicating that GLP-1RAs may exert immunomodulatory effects, including upregulation of anti-inflammatory cytokines [e.g., interleukin (IL)-10] and suppression of pro-inflammatory mediators such as TNF-α, IL-6, and IL-1β[176-179]. In addition, liraglutide has been shown to activate Nrf2 signaling, thereby mitigating lipotoxicity and OxS[180]. Clinically, the LEAN trial (liraglutide 1.8 mg daily for 48 weeks) demonstrated resolution of MASH in 39% of patients receiving liraglutide compared with 9% in the placebo group, along with reduced fibrosis progression[181]. Similarly, the phase 3 ESSENCE trial reported that semaglutide (2.4 mg weekly for 72 weeks) significantly increased rates of steatohepatitis resolution and fibrosis improvement compared with placebo[182]. Based on these findings, the United States Food and Drug Administration approved semaglutide 2.4 mg for adults with non-cirrhotic MASH and moderate-to-advanced fibrosis (stages F2-F3), in combination with diet and physical activity. Furthermore, tirzepatide, a dual GLP-1/glucose-dependent insulinotropic polypeptide receptor agonist, has shown robust efficacy in MASLD/MASH, with the phase 2 SYNERGY-NASH trial demonstrating substantially higher rates of MASH resolution without worsening of fibrosis compared with placebo[183].

Sodium-glucose cotransporter-2 inhibitors (SGLT-2i) (e.g., dapagliflozin and empagliflozin) confer both metabolic and hepatic benefits in patients with T2DM and MASLD[173]. Mechanistically, SGLT-2i enhance fatty acid β-oxidation and insulin sensitivity, modulate gut microbiota, and attenuate inflammation, OxS, lipogenesis, and fibrosis[184]. Evidence from randomized controlled trials and meta-analyses demonstrates significant reductions in liver fat content, as assessed by magnetic resonance imaging-proton density fat fraction (MRI-PDFF), compared with control interventions[185]. For instance, the E-LIFT trial (empagliflozin 10 mg daily for 20 weeks) reported a significant reduction in MRI-PDFF relative to placebo[186].

The rationale for antioxidant supplementation in MASLD is supported by consistent evidence showing reduced hepatic antioxidant capacity in affected individuals[187]. GSH, a critical intracellular antioxidant, plays an essential role in redox balance and detoxification processes[188]. A pilot study in Japanese patients with MASLD reported that oral GSH administration (300 mg/day for 4 months) significantly reduced alanine aminotransferase levels and hepatic steatosis[189]. N-acetylcysteine (NAC), a thiol-containing compound and GSH precursor, exerts both antioxidant and anti-inflammatory effects by replenishing intracellular GSH levels and enhancing GSH reductase activity. Findings from both preclinical and clinical studies suggest that NAC improves lipid metabolism, reduces liver inflammation, and attenuates steatosis in MASLD[190-192].

Pirfenidone, an anti-fibrotic agent approved for the treatment of idiopathic pulmonary fibrosis and other fibrotic disorders[193], has also demonstrated therapeutic potential in experimental models of MASLD. Its hepatoprotective effects are thought to involve attenuation of OxS and inflammation through activation of Nrf2 signaling and inhibition of the NF-κB pathway[194].

CONCLUSION

The pathogenesis of MASLD is multifactorial and involves the disruption of numerous physiological homeostatic mechanisms. A HFD is a well-established risk factor, and its deleterious effects are largely mediated through alterations in gut microbiota and induction of OxS. Gut dysbiosis not only disrupts microbial metabolite profiles but also impairs intestinal barrier integrity, promotes endotoxemia, and activates pro-inflammatory signaling pathways, thereby exacerbating hepatic OxS and metabolic disturbances. OxS, in particularly, plays a central role in MASLD progression. HFD-induced lipid overload and microbial imbalance contribute to redox dysregulation and increased production of ROS and lipotoxic intermediates within hepatocytes. This oxidative burden results in cellular macromolecule damage, hepatocellular inflammation, and fibrogenesis. Together, HFD, gut dysbiosis, and OxS form a synergistic triad that drives the progression of MASLD to more advanced and clinically significant stages. Recent experimental studies have underscored the therapeutic potential of targeting OxS in MASLD. Natural compounds such as quercetin and resveratrol have shown promise due to their potent antioxidant properties. Pharmaceutical agents, including GLP-1RAs and SGLT-2i have also demonstrated beneficial effects through modulation of redox and inflammatory pathways. In addition, lifestyle interventions, particularly exercise and antioxidant-rich dietary modifications, represent practical and effective strategies for restoring redox balance. Despite these encouraging findings, the precise molecular targets and underlying cellular mechanisms remain incompletely understood. Further mechanistic research and well-designed clinical trials are necessary to confirm the therapeutic efficacy of antioxidant-based interventions in MASLD. While current evidence highlights the pivotal roles of OxS, gut dysbiosis, and HFDs in MASLD pathogenesis, several key knowledge gaps remain. Future research should aim to elucidate the precise molecular mechanisms linking OxS to hepatocellular injury, fibrosis, and disease progression in MASLD. Additionally, it is important to investigate the bidirectional relationship between gut microbiota alterations and hepatic redox homeostasis, particularly in human cohorts. Identifying and validating novel redox-sensitive biomarkers to improve early diagnosis and monitor therapeutic response is another crucial area. Furthermore, well-powered, multicenter clinical trials are needed to assess the efficacy and safety of antioxidant-based therapies, including natural bioactive compounds and pharmaceutical agents. Finally, exploring combinatory interventions that integrate dietary, lifestyle, and pharmacological strategies is essential to enhance therapeutic outcomes and personalize MASLD treatment. A deeper mechanistic understanding and translational validation of antioxidant-targeted strategies may pave the way for more effective, evidence-based clinical management of MASLD.