Phytosterols in human health: Biochemical mechanisms of action and disease-modulating effects

Abstract

Phytosterols are plant-derived sterols structurally similar to cholesterol and present in vegetable oils, seeds, legumes, and whole grains. Their best-established health effect is lowering circulating low-density lipoprotein cholesterol, mainly through inhibition of intestinal cholesterol absorption. Beyond this classical role, recent studies suggest that phytosterols may influence biological processes relevant to human health. Proposed mechanisms include changes in membrane lipid organization, modulation of nuclear receptors such as liver X receptors and peroxisome proliferator-activated receptors, activation of AMP-activated protein kinase, and regulation of metabolic and inflammatory signaling pathways. Experimental and human evidence indicates possible effects on adipose tissue function, hepatic lipid accumulation, insulin sensitivity, inflammation, oxidative stress, and immune responses. These findings have increased interest in the relevance of phytosterols to obesity, metabolic dysfunction-associated steatotic liver disease, type 2 diabetes, and immune-mediated disorders such as rheumatoid arthritis. Interactions with the gut microbiota and bile acid metabolism may provide additional pathways linking phytosterol intake with systemic effects, although human evidence remains limited. Antioxidant and anti-inflammatory actions have also been linked to neuroprotective and anticancer effects, but current support is mainly from preclinical studies. This review critically summarizes mechanistic and translational evidence, with emphasis on bioavailability, interindividual variability, safety, and remaining research gaps.

Key Words: Phytosterols; Lipid metabolism; Cholesterol absorption; Molecular mechanisms; Inflammation; Oxidative stress; Metabolic disorders; Cardiovascular disease; Functional foods

Core Tip: Phytosterols are well-established cholesterol-lowering agents, but emerging evidence highlights their broader biological roles. This review provides a comprehensive synthesis of molecular mechanisms underlying phytosterol action, including modulation of liver X receptors, peroxisome proliferator-activated receptors, and AMP-activated protein kinase signaling, membrane lipid organization, and gut microbiota-bile acid interactions. These integrated pathways contribute to improved lipid and glucose metabolism, reduced inflammation, and enhanced cardiometabolic health, supporting the potential of phytosterols as multifunctional dietary bioactives beyond lipid lowering.

INTRODUCTION

Phytosterols are naturally occurring plant sterols that closely resemble cholesterol in structure and are widely found in plant-based foods such as vegetable oils, nuts, seeds, legumes, and whole grains[1-3]. The main dietary phytosterols – β-sitosterol, campesterol, and stigmasterol – contribute most of total phytosterol intake in humans and retain biological activity despite limited systemic absorption[4]. Because of their structural similarity to cholesterol, phytosterols compete with cholesterol for incorporation into intestinal micelles, reducing cholesterol absorption and lowering circulating low-density lipoprotein cholesterol (LDL-C). This cholesterol-lowering effect is well established and has been consistently demonstrated in randomized controlled trials, meta-analyses, and experimental studies, supporting the use of phytosterol-enriched foods in cardiovascular risk-reduction strategies[5-8].

In addition to their lipid-lowering properties, phytosterols are increasingly recognized as multifunctional bioactive compounds with broader physiological significance. Experimental and clinical studies demonstrate that phytosterols influence pathways related to lipid and glucose metabolism, inflammatory signaling, oxidative stress, immune regulation, and cellular homeostasis[9-12]. The underlying mechanisms include alterations in membrane lipid organization, regulation of nuclear receptors such as liver X receptors (LXRs) and peroxisome proliferator-activated receptors (PPARs), activation of AMP-activated protein kinase (AMPK), and modulation of downstream signaling pathways[13,14].

These molecular actions may account for the potential roles of phytosterols in conditions beyond dyslipidemia. Current evidence indicates involvement in adipose tissue function, hepatic lipid accumulation, and insulin sensitivity, highlighting relevance to obesity and metabolic dysfunction-associated steatotic liver disease (MASLD)[11,15]. Additionally, phytosterols exhibit immunomodulatory properties, influencing both innate and adaptive immune responses by suppressing pro-inflammatory signaling and modulating immune–metabolic interactions, with potential implications for inflammatory disorders such as rheumatoid arthritis (RA)[16,17].

Interactions between phytosterols and the gut microbiota further broaden their biological relevance. Because absorption is limited, substantial amounts reach the colon, where they may influence microbial composition, bile acid (BA) metabolism, and gut barrier function, thereby contributing to systemic metabolic and immune effects[11,18]. Antioxidant and anti-inflammatory properties of phytosterols have also been linked to neuroprotective and anticancer effects reported mainly in preclinical studies[19-21].

Despite extensive investigation, important questions remain regarding phytosterol bioavailability, interindividual variability, circulating phytosterol levels, long-term safety, and translational relevance beyond cholesterol lowering. This narrative review provides a critical synthesis of current evidence on the biochemical and molecular mechanisms underlying phytosterol action, with emphasis on linking mechanistic pathways to physiological and clinical outcomes. It examines the coordinated roles of membrane lipid modulation, LXR and PPAR signaling, AMPK activation, and the gut microbiota-BA axis in mediating the pleiotropic effects of phytosterols. In addition, it highlights circulating phytosterol levels as emerging biomarkers linking dietary exposure with metabolic responses and clinical outcomes. By integrating findings from in vitro studies, animal models, and human investigations, this review aims to provide a clinically contextualized perspective while identifying priorities for future research.

METHODOLOGY

Given the narrative and integrative nature of this review, a structured but non-systematic literature search strategy was adopted to capture multidisciplinary evidence across nutrition science, food science, and bioactive compound research, with supportive insights from biotechnology and related health fields.

Peer-reviewed literature was identified through searches of PubMed, Scopus, Web of Science, ScienceDirect, and Google Scholar conducted through February 2026. Publications from January 2000 to February 2026 were prioritized, while earlier seminal studies were included where relevant to foundational concepts.

Searches combined keywords and Boolean operators such as: (1) Phytosterols AND human health; (2) Phytosterols AND absorption; (3) Phytosterols AND metabolism; (4) Phytosterols AND bioavailability; (5) Phytosterols AND molecular mechanisms; (6) Phytosterols AND gut microbiota; (7) Phytosterols AND inflammation; (8) Phytosterols AND oxidative stress; and (9) Phytosterols AND cardiometabolic health.

Studies were selected based on scientific relevance, methodological quality, recency, and contribution to the mechanistic or translational themes of the review. Priority was given to randomized controlled trials, meta-analyses, systematic reviews, and well-designed experimental studies. Relevant regulatory or institutional reports published in English were also considered.

As a narrative review, this work does not aim to provide exhaustive systematic coverage of all available literature, and some degree of selection bias inherent to qualitative synthesis cannot be fully excluded.

STRUCTURE AND BIOCHEMICAL PROPERTIES OF PHYTOSTEROLS

Phytosterols are triterpenoid compounds belonging to the sterol family and share a common cyclopentanoperhydrophenanthrene ring structure with cholesterol. This core structure consists of four fused rings featuring a hydroxyl group at the C3 position and a double bond between C5 and C6, which are essential for their sterol-like behavior within biological membranes[13,22]. The primary structural distinction between phytosterols and cholesterol lies in the aliphatic side chain at the C17 position. Most phytosterols contain additional methyl or ethyl groups at C24, which significantly influence their physicochemical properties, intestinal handling, and biological activity[18]. Phytosterols share the core sterol nucleus of cholesterol but differ mainly in side-chain substitutions and unsaturation patterns, structural features that influence their intestinal absorption, membrane behavior, and biological activity.

Among dietary phytosterols, β-sitosterol, campesterol, and stigmasterol are the most abundant and biologically relevant. The β-sitosterol contains an ethyl group at C24, campesterol contains a methyl group at the same position, while stigmasterol additionally possesses a double bond between C22 and C23. Despite their apparent subtlety, these structural variations markedly affect sterol solubility, membrane affinity, and interaction with sterol transporters and nuclear receptors[11,13]. Compared with cholesterol, phytosterols display lower aqueous solubility and reduced affinity for intestinal micelles, contributing to their limited absorption and rapid efflux back into the intestinal lumen[23].

At the biochemical level, phytosterols incorporate into cellular membranes, where they influence membrane fluidity, lipid raft formation, and cholesterol distribution. Experimental studies demonstrate that phytosterols can partially replace cholesterol in phospholipid bilayers, altering membrane order and modulating the function of membrane-associated proteins, including receptors and transporters involved in lipid metabolism and inflammatory signaling[11,16].

These membrane-level effects are increasingly recognized as a key mechanism underlying the pleiotropic biological actions of phytosterols beyond cholesterol displacement.

Beyond their membrane-related properties, phytosterols modulate key molecular regulators of lipid and metabolic homeostasis. Structural similarities to cholesterol allow phytosterols to serve as ligands or modulators of nuclear receptors such as LXRs and PPARs, thereby influencing gene expression related to cholesterol efflux, fatty acid oxidation, and inflammatory responses[13,17]. These biochemical properties provide a mechanistic basis for the diverse metabolic and anti-inflammatory effects attributed to phytosterols in experimental and clinical settings.

ABSORPTION, METABOLISM, AND BIOAVAILABILITY OF PHYTOSTEROLS

The absorption and systemic availability of phytosterols are tightly regulated and significantly lower than those of cholesterol, which reflects specialized intestinal and hepatic transport mechanisms. Under normal dietary conditions, less than 5% of ingested phytosterols are absorbed vs approximately 50%-60% of dietary cholesterol[11,18]. This limited absorption determines their biological behavior and safety profile.

In the intestinal lumen, phytosterols and cholesterol are incorporated into mixed micelles in the presence of BAs. Due to their lower solubility within micelles, phytosterols are less efficiently transported across the brush-border membrane of enterocytes[23]. Uptake of sterols into enterocytes is mediated primarily by Niemann-Pick C1-Like 1 (NPC1 L1), a transmembrane transporter that facilitates sterol internalization. Although NPC1 L1 can transport both cholesterol and phytosterols, it exhibits a higher affinity for cholesterol. This contributes to preferential cholesterol absorption over plant sterols[13,24,25].

Inside the enterocytes, phytosterols are rapidly released back into the intestinal lumen by the ATP-binding cassette transporters ABCG5 and ABCG8, which function as a heterodimer and serve as a critical protective mechanism against excessive phytosterol accumulation[18,26]. These transporters also operate in hepatocytes, where they mediate biliary secretion of phytosterols, which limits systemic exposure. Genetic defects in ABCG5 or ABCG8 result in sitosterolemia, a rare disorder characterized by markedly elevated plasma phytosterol levels and premature atherosclerosis, which shows the importance of these transporters in sterol homeostasis[25].

Phytosterols that escape efflux undergo limited esterification by acyl-CoA:cholesterol acyltransferase 2 and are incorporated into chylomicrons with much lower efficiency than cholesterol. Consequently, plasma phytosterol concentrations remain low under normal physiological conditions[18]. Recent mechanistic studies further indicate that phytosterols may modulate the expression and activity of sterol transporters and metabolic regulators, including NPC1 L1, ABCG5/ABCG8, and LXRs. This suggests feedback mechanisms affecting both phytosterol and cholesterol metabolism[11,17].

Beyond physiological determinants, the extraction and processing methods used to obtain phytosterols can influence their composition, bio-accessibility, and subsequent metabolic handling. Conventional solvent extraction, supercritical fluid extraction, and enzymatic approaches differ in their ability to preserve native phytosterol structures and to limit the formation of oxidized phytosterol derivatives, which may exhibit altered absorption and biological activity[16]. Variations in phytosterol preparation may affect solubility, micellar incorporation, and interactions with intestinal transporters, thereby contributing to differences in absorption efficiency and systemic exposure[18]. These factors may partly account for variability in experimental and clinical outcomes and should be considered when interpreting studies on phytosterol bioavailability and metabolic effects.

Phytosterol bioavailability is influenced by multiple dietary and host-related factors, including food matrix, fat content, chemical form (free sterols vs esterified sterols), gut microbiota composition, and genetic variability in sterol transporters[16,25]. Advances in formulation strategies, such as esterification, nanoemulsions, and encapsulation technologies, have been explored to enhance bioavailability and functional efficacy. However, their long-term physiological implications remain to be fully clarified[11]. Clinical responses may also differ according to formulation, food matrix, emulsification system, and delivery technology, which underscores the need for standardized comparisons across studies.

Given the tightly regulated absorption and systemic handling of phytosterols, understanding their circulating levels and clinical implications is essential for interpreting their biological effects in humans.

CIRCULATING PHYTOSTEROLS AND CLINICAL RELEVANCE

Based on these pharmacokinetic characteristics, the assessment of circulating phytosterol levels provides information about their systemic effects and clinical relevance.

While dietary intake of phytosterols has been widely studied, their circulating concentrations and clinical implications remain less clearly defined. Under normal physiological conditions, plasma phytosterol levels are extremely low, typically representing less than 1% of circulating sterols. This is due to highly efficient efflux mechanisms mediated by ATP-binding cassette transporters ABCG5 and ABCG8[18,13,27,28]. These transporters actively limit systemic accumulation by promoting the return of absorbed phytosterols to the intestinal lumen and enhancing biliary excretion[18,27].

Importantly, circulating phytosterol concentrations do not directly reflect dietary intake but rather indicate individual differences in sterol absorption efficiency and transporter activity[8,18]. Elevated plasma phytosterol levels have been observed in individuals with increased intestinal absorption of sterols. They have also been more markedly found in patients with sitosterolemia, a rare genetic disorder caused by mutations in ABCG5 or ABCG8[25,29]. This condition is characterized by excessive accumulation of phytosterols in plasma and tissues and is associated with premature atherosclerosis, which highlights the importance of tightly regulated sterol homeostasis[13,30].

In clinical and epidemiological studies, the relationship between circulating phytosterol levels and cardiovascular risk is controversial. Some studies suggest a positive correlation between elevated plasma phytosterols and cardiovascular risk. Other reports show neutral or even protective associations[17,18,31]. These discrepancies likely reflect differences in study design, population characteristics, and the interpretation of phytosterols as biomarkers of cholesterol absorption rather than direct causal agents[8].

From a methodological perspective, accurate quantification of circulating phytosterols requires sensitive analytical techniques, such as gas chromatography – mass spectrometry or liquid chromatography – mass spectrometry, which enable discrimination between cholesterol and structurally similar plant sterols[13,18]. Despite their importance, such measurements are not normally found in many clinical trials investigating phytosterol supplementation[8,32].

Overall, consideration of circulating phytosterol levels provides important insight into interindividual variability in response to phytosterol intake and may improve the interpretation of clinical outcomes. Future studies should incorporate standardized measurement of plasma phytosterols to better define their role as biomarkers and to clarify their long-term clinical significance[17,11,33].

MOLECULAR MECHANISMS OF ACTION OF PHYTOSTEROLS

Phytosterols exert diverse biological effects through complementary molecular mechanisms that regulate cellular signaling and metabolic homeostasis. These actions involve both membrane-level processes and intracellular pathways, including modulation of lipid raft organization and regulation of key transcription factors and kinases such as PPARs, AMPK, and LXRα. Through these interconnected networks, phytosterols influence cholesterol transport, lipid metabolism, inflammatory responses, and glucose homeostasis, providing a mechanistic basis for their potential roles in metabolic and inflammatory disorders.

Membrane-mediated signaling and lipid raft modulation

Phytosterols exert important effects at the level of cellular membranes. Due to their structural similarity to cholesterol, they can partially replace cholesterol within phospholipid bilayers, which alters membrane fluidity and the organization of lipid rafts – cholesterol-rich microdomains that function as signaling platforms[16]. Incorporation of phytosterols into the plasma membrane disrupts lipid packing order and modifies membrane mechanical properties, which may interfere with translocation of the p67 subunit and suppress NADPH oxidase (NOX) activation, leading to reduced reactive oxygen species (ROS) generation. Attenuation of ROS signaling may subsequently downregulate the NLR family pyrin domain containing 3 inflammasome, supporting a membrane-mediated anti-inflammatory mechanism[34]. Remodeling of lipid rafts may also influence membrane-associated receptors and signaling molecules involved in inflammation, immune cell activation, and cell proliferation, potentially contributing to anti-inflammatory and antiproliferative effects[11].

Regulation of LXRs

LXRs (LXRα and LXRβ) are cholesterol-sensing nuclear receptors that regulate genes involved in cholesterol efflux, BA synthesis, and lipid transport. They have therefore attracted interest as therapeutic targets in neurodegenerative and cardiometabolic diseases characterized by disturbed sterol homeostasis and inflammation[35-37].

Phytosterols and some oxidized derivatives have been reported to interact with LXR signaling, directly or indirectly, leading to upregulation of ATP-binding cassette transporters such as ATP-binding cassette transporter A1 and ABCG1, which promote cholesterol efflux from peripheral tissues[13,18]. LXR-responsive sterols may also enhance ApoE-mediated lipid trafficking between astrocytes and neurons and promote neuronal cholesterol turnover through upregulation of CYP46A1[38]. In the liver, phytosterol derivatives have been shown to increase expression of LXRα and cholesterol 7α-hydroxylase, thereby increasing fecal BA excretion[39]. Collectively, these findings suggest that the LXRα-cholesterol 7α-hydroxylase-BA pathway may contribute to the cholesterol-lowering effects of phytosterols. However, excessive LXR activation has also been linked to hepatic lipogenesis, underscoring the importance of context-dependent regulation[11].

Activation of AMPK

AMPK is a central regulator of cellular energy homeostasis that responds to changes in the AMP/ATP ratio. Experimental studies suggest that phytosterols can activate AMPK signaling, either directly or through upstream kinases, resulting in suppression of lipogenesis and stimulation of fatty acid oxidation[11]. β-sitosterol and stigmasterol have been reported to interact with the allosteric site of AMPK in computational or experimental models[40]. In preclinical studies, β-sitosterol modulated AMPK signaling and reduced hepatic lipid accumulation in non-alcoholic fatty liver disease models[41], while stigmasterol attenuated neuroinflammation in APP/PS1 mice and suppressed microglial responses to Aβ42 oligomers through the AMPK/nuclear factor kappa B (NF-κB) pathway[42].

Phytosterols may also regulate hepatic lipid metabolism through AMPK-dependent downregulation of sterol regulatory element-binding protein-1c and fatty acid synthase. This suppresses de novo lipogenesis and promotes fatty acid oxidation[11]. Similarly, stigmasterol combined with gastrodin reduced lipid accumulation and modulated genes related to lipid metabolism via the AMPK/sterol regulatory element-binding protein-1c pathway in high-fat diet rat models[43]. These findings support AMPK as a plausible mediator of the metabolic effects of phytosterols, although confirmation in humans remains limited.

Modulation of PPARs

PPARα, PPARγ, and PPARδ are transcription factors that regulate lipid oxidation, adipogenesis, glucose metabolism, and inflammatory responses. Experimental evidence indicates that phytosterols can modulate PPAR activity, particularly PPARα and PPARγ, leading to enhanced fatty acid oxidation, improved insulin sensitivity, and attenuation of inflammatory signaling[17,44]. β-sitosterol has also been proposed as a candidate modulator of PPARγ2 and NLR family pyrin domain containing 3-dependent pyroptosis in experimental models of ischemic cardiovascular injury[45].

These effects are relevant to metabolic disorders in which impaired PPAR signaling contributes to insulin resistance and lipid accumulation. By influencing PPAR-dependent gene expression, phytosterols may help restore metabolic homeostasis in tissues such as liver, adipose tissue, and skeletal muscle. PPARγ activation can also enhance expression of ATP-binding cassette transporter A1 and promote cholesterol efflux from macrophages through induction of LXRα signaling[46]. Additional studies suggest that phytosterols may improve glucose metabolism through coordinated effects involving AMPK activation, modulation of PPARγ signaling, and suppression of inflammation that impairs insulin action[11]. Computational analyses further predict interactions with AMPK-related and PPAR-related targets, including PPARγ, PPARδ, AMPK, and LXRα[47]. These in silico observations are useful for generating hypothesis, but they do not alone confirm pathway activation or metabolic efficacy.

The overall physiological response to phytosterol intake likely reflects integration of these pathways rather than a single mechanism. Recent advances have also highlighted the gut microbiota as an additional mediator of phytosterol biological activity.

ROLE OF PHYTOSTEROLS IN THE GUT–METABOLISM AXIS

Phytosterols and gut microbiota: A bidirectional relationship

Phytosterols – particularly β-sitosterol, campesterol, and stigmasterol – are plant-derived sterols structurally similar to cholesterol and widely consumed through plant-based foods and fortified products[48,49]. Their best-established action is the reduction of intestinal cholesterol absorption through displacement from mixed micelles and modulation of the NPC1 L1 transporter. This strategy is recognized in dietary approaches for hypercholesterolemia management[18,50]. Beyond this effect, growing evidence suggests interactions between phytosterols and the gut microbiota, although current support is derived predominantly from preclinical studies.

Animal studies have reported that phytosterol supplementation can alter microbial composition, including shifts in the Firmicutes/Bacteroidetes ratio and changes in specific taxa such as Bacteroidetes and Actinobacteria[51]. Experimental microbiota-depletion and fecal microbiota transplantation models further suggest that part of the lipid-lowering response to phytosterols may depend on microbiota[52]. In addition, microbial metabolism of phytosterols may generate secondary sterol metabolites with potential biological activity, although these pathways remain incompletely characterized[53]. While these findings are informative, their direct relevance to humans remains uncertain and should be interpreted cautiously.

BA signaling and hepatic metabolic regulation

One proposed mechanism linking phytosterols, gut microbiota, and host metabolism involves BA transformation and enterohepatic signaling. Gut microbes convert primary BAs into secondary BAs through bile salt hydrolase and related enzymatic activities. The influences signaling pathways mediated by the farnesoid X receptor and Takeda G protein-coupled receptor 5[54,55]. In preclinical models, phytosterol intake has been associated with alterations in BA composition and hepatic pathways related to lipid metabolism and cholesterol disposal[51,52].

These observations suggest that microbiota-dependent BA signaling may contribute to the systemic effects of phytosterols on hepatic lipid handling and glucose regulation. However, evidence in humans remains limited. Therefore, the gut microbiota – BA axis should currently be viewed as a promising but still emerging mechanism that requires further clinical validation[56,57].

Translational perspectives and interindividual variability

Despite encouraging evidence, translation of phytosterol-microbiome interactions into human health outcomes remains incomplete. Human intervention studies have produced less consistent findings than animal models, with some reporting modest or selective changes in microbiota composition after plant sterol or stanol supplementation[58,59]. These discrepancies likely reflect substantial interindividual variability in baseline microbiota composition, habitual diet, metabolic status, genetics, intervention duration, and phytosterol formulation or bioavailability[50].

Host factors affecting sterol transport, including ABCG5/ABCG8 activity, may further modify circulating phytosterol levels and physiological responses. Rare disorders such as sitosterolemia illustrate the importance of tightly regulated sterol handling and demonstrate that responses to phytosterol exposure can be variable[60]. Emerging evidence also suggests possible associations between phytosterol intake, microbial diversity, and short-chain fatty acid production. These relationships require confirmation using adequate clinical studies[61].

Future research should prioritize standardized human trials integrating microbiome profiling, metabolomics, circulating phytosterol measurements, and clinically meaningful cardiometabolic outcomes. A systems-level approach that considers dietary exposure, microbial ecology, host genetics, and metabolic phenotype will be essential to define which individuals are most likely to benefit from phytosterol interventions.

Collectively, these interconnected pathways illustrate how phytosterols may influence metabolic and inflammatory processes at molecular and systemic levels, although the strength of evidence differs substantially between preclinical and human studies. The principal mechanisms through which phytosterols modulate metabolic and inflammatory pathways are summarized in Figure 1.

Figure 1 Molecular mechanisms underlying the metabolic and anti-inflammatory effects of phytosterols. Phytosterols regulate multiple cellular signaling pathways involved in metabolic homeostasis and inflammation. These mechanisms include activation of liver X receptors, which enhances cholesterol efflux through ATP-binding cassette transporter A1 and ABCG1 and promotes reverse cholesterol transport; modulation of peroxisome proliferator-activated receptors (α/γ), which improves fatty acid oxidation and insulin sensitivity; and activation of AMP-activated protein kinase, resulting in suppression of lipogenesis and stimulation of energy metabolism. In addition, phytosterols alter membrane lipid raft organization, influencing receptor-mediated signaling and inflammatory pathways. Emerging evidence also indicates that phytosterols modulate gut microbiota composition and bile acid signaling through pathways involving the farnesoid X receptor and Takeda G protein-coupled receptor 5, contributing to improved metabolic regulation. Collectively, these mechanisms lead to reduced low-density lipoprotein cholesterol levels, decreased hepatic lipid accumulation, improved insulin sensitivity and glucose uptake, and attenuation of systemic inflammation, ultimately supporting cardiometabolic health. ABCA1: ATP-binding cassette transporter A1; ACC: Acetyl-CoA carboxylase; AMPK: AMP-activated protein kinase; FXR: Farnesoid X receptor; LDL-C: Low-density lipoprotein cholesterol; LXR: Liver X receptors; PPAR: Peroxisome proliferator-activated receptors; SREBP-1c: Sterol regulatory element-binding protein-1c; TGR5: Takeda G protein-coupled receptor 5.

ANTI-INFLAMMATORY AND ANTIOXIDANT ACTIONS

Chronic low-grade inflammation and oxidative stress are central features of many metabolic, cardiovascular, and neurodegenerative disorders. Increasing evidence indicates that phytosterols exert anti-inflammatory and antioxidant effects that contribute to their broader health benefits beyond cholesterol lowering. These actions are mediated through modulation of inflammatory signaling pathways, regulation of redox homeostasis, and stabilization of cellular membranes.

At the molecular level, phytosterols suppress activation of key pro-inflammatory transcription factors, particularly NF-κB, which regulates the expression of cytokines, chemokines, and adhesion molecules involved in inflammatory responses[11,16]. In vitro and animal studies demonstrate that phytosterol treatment reduces the production of inflammatory mediators, including tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and C-reactive protein, while promoting anti-inflammatory cytokine profiles. These effects are partially attributed to interference with membrane-associated signaling events and attenuation of toll-like receptor-mediated pathways[62,63].

Phytosterols also exhibit antioxidant properties by modulating oxidative stress pathways and improving cellular redox balance. Experimental evidence suggests that phytosterols reduce ROS and lipid peroxidation. They also enhance the activity of endogenous antioxidant enzymes, including superoxide dismutase, catalase, and glutathione peroxidase (GPx)[6,16,17,64]. These effects may involve activation of the nuclear factor erythroid 2-related factor 2 pathway and suppression of NOX activity[63,65,66].

Experimental studies indicate that phytosterols promote nuclear factor erythroid 2-related factor 2 signaling, which leads to increased expression of antioxidant enzymes such as heme oxygenase-1, superoxide dismutase, catalase, and GPx. This effect can limit oxidative damage and improve redox balance[65,67]. In parallel, phytosterols may attenuate NOX activation by modifying membrane lipid organization and lipid raft assembly, which results in reduced superoxide production and downstream oxidative signaling[51,66]. These complementary mechanisms provide a basis for protective effects against endothelial dysfunction, hepatic steatosis, insulin resistance, and chronic inflammation, although most evidence remains preclinical[68,69].

In addition to direct antioxidant actions, phytosterols may indirectly reduce oxidative stress by improving lipid profiles and decreasing the susceptibility of low-density lipoprotein particles to oxidative modification. Reduced LDL oxidation represents a key mechanism linking phytosterol intake to attenuation of atherosclerotic processes and endothelial dysfunction[70]. Clinical and observational studies further support these findings, reporting associations between higher phytosterol intake and lower circulating markers of inflammation and oxidative stress in populations at risk of cardiometabolic disease[17].

Collectively, the anti-inflammatory and antioxidant properties of phytosterols complement their metabolic actions and provide a mechanistic basis for protective effects in chronic inflammatory conditions such as RA. These pleiotropic actions underscore the potential of phytosterols as dietary modulators of inflammation and oxidative stress in disease prevention strategies.

Molecular docking analyses have reported predicted interactions between avocado-derived bioactive compounds and proteins associated with inflammation, oxidative stress, metabolic regulation, and apoptosis, including cyclooxygenase-2, GPx, α-glucosidase, and Bcl-xL[71]. These findings suggest candidate molecular targets for further study, but they require experimental validation.

ROLES IN CARDIOVASCULAR AND METABOLIC DISEASES

Cardiovascular and metabolic diseases remain to be the leading causes of morbidity and mortality worldwide and are driven by interconnected processes including dyslipidemia, insulin resistance, chronic inflammation, and oxidative stress. Phytosterols have been extensively investigated in this regard because of their well-established cholesterol-lowering effects and broader metabolic actions. Many of these responses involve shared pathways such as AMPK activation, PPAR modulation, and anti-inflammatory signaling, as previously discussed. These interconnected molecular and metabolic pathways converge to influence cardiometabolic health at the systemic level, as summarized in Figure 2. The principal biological mechanisms, relative strength of evidence, and reported health outcomes associated with phytosterols across major disease domains are summarized in Table 1.

Figure 2 Integrated effects of phytosterols in cardiometabolic health. Dietary phytosterols derived from plant-based foods act across multiple target tissues, including the liver, intestine, adipose tissue, skeletal muscle, and immune cells, to exert coordinated metabolic effects. These actions lead to reduced intestinal cholesterol absorption, decreased hepatic lipid accumulation, improved insulin sensitivity, enhanced glucose utilization, and attenuation of systemic inflammation. Collectively, these integrated physiological and clinical outcomes contribute to improved cardiometabolic health and reduced risk of cardiovascular and metabolic diseases. LDL-C: Low-density lipoprotein cholesterol.

Table 1 Summary of principal biological mechanisms, evidence strength, and reported health outcomes of phytosterols across major disease domains.

Domain	Main mechanisms	Evidence strength	Reported outcomes
Cardiovascular health	Reduced intestinal cholesterol absorption; LDL-C lowering; improved endothelial function	Strong (randomized controlled trials/meta-analyses)	Lower LDL-C; improved vascular markers
Diabetes/glucose metabolism	AMP-activated protein kinase activation; peroxisome proliferator-activated receptors modulation; reduced inflammation; improved insulin signaling	Moderate	Improved insulin sensitivity; better glycemic markers
Metabolic dysfunction-associated steatotic liver disease/fatty liver	Reduced lipogenesis; enhanced fatty acid oxidation; anti-inflammatory effects	Moderate (mainly preclinical)	Reduced hepatic lipid accumulation
Obesity	Adipocyte metabolism modulation; anti-inflammatory effects	Limited-moderate	Improved metabolic profile; uncertain weight loss
Gut–metabolism axis	Microbiota shifts; bile acid signaling (farnesoid X receptor/Takeda G protein-coupled receptor 5); short-chain fatty acid-related effects	Emerging (mainly preclinical)	Potential metabolic benefits
Antioxidant/inflammation	Nuclear factor kappa B suppression; nuclear factor erythroid-2-related factor 2 activation; reduced NADPH oxidase activity	Moderate (mostly experimental)	Reduced oxidative stress and inflammation
Anticancer	Cell-cycle arrest; apoptosis; membrane signaling effects	Preliminary (preclinical)	Mechanistic potential only
Neuroprotection	Anti-inflammatory and antioxidant actions; lipid signaling	Preliminary (preclinical)	Mechanistic potential only

LDL-C: Low-density lipoprotein cholesterol.

Cardiovascular evidence: Strongest clinical support

The most robust evidence for phytosterol efficacy against cardiovascular risk is through lowering circulating LDL-C. Randomized controlled trials and meta-analyses consistently show that intake of approximately 2 g/day significantly reduces LDL-C, regardless of diet or statin therapy[23,32,43]. Improvements in vascular markers, including endothelial function and arterial stiffness, have also been reported[18].

Additional benefits may include reduced LDL oxidation, favorable changes in lipoprotein subfractions, and attenuation of inflammatory or oxidative pathways relevant to atherogenesis[11,16,70]. However, despite consistent lipid-lowering effects, direct evidence from long-term randomized trials showing reductions in major cardiovascular events remains limited. Therefore, current support for phytosterols in cardiovascular prevention is strongest for validated risk markers rather than clear clinical outcomes[68].

Metabolic disorders: Emerging but less definitive evidence

Compared with cardiovascular outcomes, evidence for disease-specific metabolic benefits remains vague and is supported only by observational or short-term intervention studies. While these findings are promising, clinical evidence is lower than LDL-C reduction.

Phytosterols and fatty liver disease

MASLD is characterized by hepatic lipid accumulation, insulin resistance, oxidative stress, and chronic inflammation. Because these pathways overlap with known actions of phytosterols, interest has grown in their potential hepatic benefits[69,72].

Animal studies consistently show reductions in hepatic lipid accumulation and improvements in inflammatory and oxidative markers following phytosterol supplementation[11,73-76]. Limited human data suggests possible improvements in liver enzymes and metabolic parameters, but adequate liver-specific clinical trials with long-term outcomes are lacking[75,77]. Accordingly, evidence for MASLD remains promising but preliminary.

Phytosterols and obesity

Obesity involves excess adipose tissue expansion, low-grade inflammation, and metabolic dysregulation[78,79]. Experimental studies indicate that phytosterols may influence adipocyte metabolism, reduce adiposity, and improve inflammatory status in preclinical models[11,62,80]. Observational human studies report associations between higher phytosterol intake and improved metabolic markers; however, direct and sustained effects on body weight or adiposity in controlled clinical trials are still uncertain[9,63,81]. Thus, phytosterols should be viewed as supportive dietary components for metabolic health rather than primary agents for weight-loss.

Phytosterols and diabetes

Type 2 diabetes is characterized by impaired insulin sensitivity, altered glucose metabolism, and chronic inflammation. Experimental evidence suggests that phytosterols may enhance insulin signaling, improve glucose utilization, and modulate inflammatory pathways in six studies[67,82-86]. Potential indirect effects through lipid improvement and gut microbiota interactions have also been proposed[51,87].

Human evidence is encouraging but still limited. Some studies associate higher phytosterol intake with improved glycemic parameters and lower diabetes risk, particularly in metabolically vulnerable populations. Well-designed trials specifically targeting glycemic outcomes remain scarce[17,88,89]. Therefore, evidence for diabetes-related benefits should currently be considered inconclusive.

Overall perspective

Collectively, phytosterols provide their strongest and most consistent clinical benefit through LDL-C lowering and improvement of validated cardiovascular risk markers. By contrast, evidence for MASLD, obesity, and diabetes is biologically supportive, but remains less definitive and requires larger, longer-term, disease-specific human trials. Long-term safety and cardiovascular outcome studies also remain important priorities for future research[6,68,90].

ANTICANCER AND CELL-REGULATORY EFFECTS

Beyond their established cardiometabolic benefits, phytosterols have attracted interest for potential anticancer and cell-regulatory properties. Experimental studies indicate that phytosterols may influence cellular processes relevant to tumor biology, including proliferation, apoptosis, cell-cycle regulation, inflammation, and oxidative stress. These findings have been reported mainly in cell culture and animal models involving colorectal, breast, prostate, and liver cancers[21,91,92].

At the cellular level, phytosterols – particularly β-sitosterol – have been shown to reduce cancer cell proliferation and induce cell-cycle arrest at the G0/G1 or G2/M phases, depending on model system and exposure conditions[93,94]. Proposed mechanisms include modulation of cyclins, cyclin-dependent kinases, and regulatory proteins such as p21 and p27. Phytosterols have also been reported to promote apoptosis through mitochondrial pathways, caspase activation, and regulation of Bcl-2 family proteins[95]. However, these observations are derived primarily from experimental systems and should not be interpreted as evidence of clinical anticancer efficacy.

Anti-inflammatory and antioxidant actions may further contribute to these effects. In preclinical models, phytosterols can suppress NF-κB signaling, reduce pro-inflammatory cytokine production, and decrease oxidative stress markers, which creates a less favorable environment for tumor progression[11,62]. Membrane-related mechanisms have also been proposed. Altered cholesterol content and lipid raft organization may influence growth factor signaling pathways such as epidermal growth factor receptor and phosphatidylinositol 3-kinase/protein kinase B[21,96]. These mechanisms remain biologically sound but incompletely validated in humans.

Human evidence remains limited. Observational studies suggest possible inverse associations between dietary phytosterol intake and risk of some cancers, particularly colorectal and breast cancer, but findings are inconsistent and subject to residual confounding[17,97,98]. At present, phytosterols should be viewed as promising bioactive compounds for further investigation rather than established anticancer interventions. Well-designed translational and clinical studies are needed to clarify dose-response relationships, tissue specificity, and potential interactions with standard therapies.

NEUROPROTECTIVE EFFECTS AND GUT-BRAIN INTERACTIONS

Interest has also expanded to the potential neuroprotective effects of phytosterols. Neurodegenerative disorders such as Alzheimer’s and Parkinson’s diseases involve neuroinflammation, oxidative stress, mitochondrial dysfunction, and altered lipid metabolism – pathways that may theoretically be influenced by phytosterols[99]. However, current evidence is derived predominantly from in vitro and animal studies.

Experimental studies suggest that phytosterols may modify membrane lipid organization, influence neuronal cholesterol homeostasis, and affect signaling pathways related to synaptic function and cell survival[99-101]. Additional preclinical work indicates that phytosterols can reduce microglial activation, suppress inflammatory mediators such as TNF-α and IL-1β, and enhance antioxidant defenses in neural tissues[42,65,102,103]. These findings support biological plausibility but do not yet establish therapeutic efficacy in humans.

Some studies further suggest that phytosterols may affect amyloid-related pathways by modulating cholesterol-rich lipid rafts or interacting with liver X receptor signaling, potentially influencing amyloid precursor protein processing and cholesterol efflux[37,104,105]. Likewise, gut microbiota modulation has been proposed as an indirect route linking phytosterols to neural function through systemic inflammation and gut-brain signaling[102,106-108]. These mechanisms remain exploratory and require substantial validation.

Although the emerging evidence is encouraging, there is currently insufficient clinical evidence to support phytosterols as established agents for prevention or treatment of neurodegenerative disease. Future human studies should determine bioavailability, blood-brain barrier relevance, effective doses, long-term safety, and clinically meaningful neurological outcomes.

EMERGING BIOLOGICAL ROLES AND IMMUNOMODULATORY EFFECTS

Immunomodulatory properties of phytosterols

The immune system is closely influenced by lipid metabolism, membrane composition, and redox balance, all of which may be affected by dietary sterols. Beyond their metabolic actions, phytosterols have attracted interest as potential modulators of innate and adaptive immune responses through anti-inflammatory signaling, regulation of immune cell activation, and effects on lipid-dependent immune pathways[109-111]. However, current evidence is derived predominantly from experimental studies, and human confirmation remains limited.

At the cellular level, phytosterols may alter membrane lipid organization and lipid raft composition. Because receptors such as toll-like receptors, T-cell receptors, and cytokine receptors are localized within cholesterol-rich microdomains, partial replacement of cholesterol with phytosterols could influence receptor clustering and downstream signaling, which may attenuate inflammatory activation[16,66,112]. Phytosterols have also been reported to suppress NF-κB signaling and reduce production of mediators such as TNF-α, IL-6, and IL-1β and also improve redox balance[11,112]. In addition, modulation of LXR and PPAR pathways has been proposed as a mechanism linking sterol metabolism with inflammatory gene regulation in immune cells[13,66]. These findings are promising but should not be interpreted as established clinical immunomodulatory effects.

Some studies further suggest that phytosterols may influence adaptive immunity, including T-cell activation and differentiation, although these effects appear to be insufficiently characterized in humans[16]. Indirect effects through gut microbiota composition and intestinal barrier function have also been proposed[11,105].

Available human data are limited to small intervention or observational studies reporting reductions in systemic inflammatory markers and improved metabolic profiles. Overall, phytosterols should be regarded as promising dietary modulators of immune homeostasis rather than established immunotherapeutic agents[11,17,113].

Effects on innate and adaptive immune responses

Innate and adaptive immune responses depend on membrane organization and intracellular metabolic signaling. Because of their structural similarity to cholesterol, phytosterols may influence both arms of the immune system through membrane-related, metabolic, and anti-inflammatory mechanisms[66].

Innate immune responses: Experimental studies indicate that phytosterols can attenuate inflammatory signaling in macrophages, dendritic cells, and related innate immune cells by modifying lipid raft organization and suppressing NF-κB or MAPK pathways[16,111,112,114]. Reductions in oxidative burst activity and ROS generation have also been reported in preclinical models[11,67].

Adaptive immune responses: In vitro findings suggest that phytosterols may modulate T-cell activation, proliferation, and cytokine profiles, with possible effects on T-helper polarization and regulatory immune responses[3,115,116]. Evidence regarding B-cell function remains sparse and largely indirect[96,117].

At present, these mechanisms should be viewed as experimentally supported but not yet clinically established, as robust human immunology studies remain scarce[113].

Phytosterols and RA

RA is a chronic autoimmune disease characterized by synovial inflammation, immune dysregulation, oxidative stress, and progressive joint damage[118,119]. Given their anti-inflammatory and metabolic properties, phytosterols have been explored as potential supportive agents in pathways relevant to RA[120,121].

Experimental evidence suggests that phytosterols can suppress NF-κB activation, reduce pro-inflammatory cytokine production, and attenuate oxidative stress – mechanisms relevant to synovial inflammation[16,112,122]. Modulation of membrane signaling and nuclear receptor pathways such as LXR and PPAR may also contribute to altered immune responses in preclinical systems[13,34,64,123,124]. Docking studies have proposed possible interactions with immune-regulatory targets such as PTPN22, although these findings remain exploratory and require experimental validation[125]. However, these results are hypothesis-generating and should not be interpreted as evidence of therapeutic efficacy.

Human evidence remains limited. Some observational data suggest that plant-based dietary patterns rich in phytosterols are associated with lower inflammatory burden, but these associations cannot be attributed to phytosterols alone and may reflect broader dietary effects[126]. Therefore, phytosterols should currently be considered supportive dietary components of interest rather than proven therapeutic agents for RA.

Overall, available evidence supports a biologically plausible role for phytosterols in immune and inflammatory pathways relevant to RA, but further mechanistic studies and well-designed clinical trials are required before firm conclusions can be drawn.

SAFETY, TOXICOLOGICAL CONSIDERATIONS, AND LIMITATIONS

Phytosterols are generally regarded as safe and have a long history of consumption through plant-based foods. Their safety profile is supported by clinical trials, regulatory evaluations, and widespread use in fortified foods, particularly at doses commonly used for cholesterol lowering (approximately 1.5-3 g/day)[18,23,96]. In healthy adults, intake within this range is generally well tolerated and not associated with clinical adverse effects on the short or the medium term. However, evidence regarding long-term exposure and hard clinical outcomes remains comparatively limited, and extended follow-up studies are needed.

A central safety consideration is the low systemic absorption of phytosterols, which is tightly controlled by intestinal and hepatic efflux transporters ABCG5 and ABCG8. These mechanisms restrict excessive accumulation of phytosterols in plasma and tissues under normal physiological conditions[27,28]. In contrast, individuals with rare genetic defects in these transporters, such as sitosterolemia, exhibit markedly elevated circulating phytosterol levels and increased risk of premature atherosclerosis[25,29,30]. Although uncommon, this condition underscores the importance of considering sterol metabolism disorders when recommending supplementation or fortified products.

Another area of ongoing debate concerns the relationship between circulating phytosterol concentrations and cardiovascular risk. Some observational studies report positive associations, whereas others describe neutral or even protective relationships[18,31,88]. Importantly, plasma phytosterol levels primarily reflect sterol absorption efficiency and transporter activity rather than dietary intake alone. Accordingly, they may function more as biomarkers of cholesterol metabolism than as independent causal risk factors. Current randomized trials do not indicate harm from recommended dietary phytosterol intake, but robust long-term cardiovascular outcome trials remain limited.

Phytosterols may also modestly reduce intestinal absorption of fat-soluble vitamins and carotenoids because of competition within mixed micelles. Clinical studies report small reductions in circulating β-carotene and, to a lesser extent, vitamins A and E; these effects are usually considered nutritionally manageable and can be minimized by adequate consumption of fruits and vegetables[23,33].

Another consideration is the oxidized phytosterol derivatives (oxyphytosterols), which can form during food processing, heating, or storage. Experimental studies suggest that some oxidized sterol derivatives may exert pro-oxidant, cytotoxic, or pro-inflammatory effects under certain conditions. However, their real-world dietary exposure, bioavailability, and clinical significance in humans remain insufficiently defined. Further research is needed to determine whether food matrix, processing conditions, or formulation strategies influence oxyphytosterol generation and biological relevance.

Safety responses may also vary across populations. Potentially susceptible groups include individuals with sitosterolemia or altered sterol transport, those with severe metabolic dysfunction, older adults with multimorbidity, and populations insufficiently studied in intervention trials such as children, pregnant or lactating women, and patients with chronic liver or kidney disease. Given this, individualized clinical conclusions should be considered until stronger evidence becomes available.

Despite substantial progress, several limitations continue to constrain understanding of phytosterol safety and efficacy. These include heterogeneity in study design, variability in formulations and doses, inconsistent measurement of circulating phytosterols, and incomplete characterization of interindividual variability related to genetics, gut microbiota composition, baseline diet, and metabolic phenotype.

Overall, phytosterols appear safe for the general population when consumed at recommended levels, but further research is needed to clarify long-term exposure effects, optimize formulations, identify susceptible subgroups, and support more personalized dietary recommendations.

FUTURE PERSPECTIVES

Phytosterols are well-established bioactive dietary constituents with a proven ability to reduce intestinal cholesterol absorption and lower circulating LDL-C. Beyond this classical effect, growing evidence suggests that their biological actions extend to broader metabolic and cellular processes, including modulation of inflammatory signaling, oxidative stress, glucose and lipid metabolism, and cellular homeostasis. At the mechanistic level, these effects involve coordinated regulation of LXRs, PPARs, AMPK, membrane lipid organization, and related downstream signaling networks.

The strongest and most consistent clinical evidence supports the use of phytosterols in cardiovascular risk management through LDL-cholesterol reduction and improvement of validated cardiometabolic risk markers. Additional benefits in conditions such as MASLD, obesity, and type 2 diabetes are biologically plausible and increasingly supported by experimental and early clinical findings, although the overall evidence base remains less definitive than for lipid lowering. Likewise, emerging data suggest potential anticancer, neuroprotective, and immunomodulatory properties, but current support is derived mainly from preclinical studies and should be interpreted cautiously.

Phytosterols are generally considered safe for the general population when consumed at recommended intake levels. Nevertheless, several issues remain important, including limited long-term exposure data, possible formation of oxidized phytosterol derivatives during processing, interindividual variability in response, and rare inherited disorders of sterol transport such as sitosterolemia. These factors support a context-specific rather than uniform approach to phytosterol use.

Despite substantial progress, important knowledge gaps remain. Long-term randomized controlled trials with hard clinical endpoints are still limited, and causal relationships between phytosterol intake and health outcomes beyond cholesterol reduction require further clarification. Future research should prioritize rigorously designed human intervention studies integrating molecular biomarkers, metabolomics and other omics platforms, circulating phytosterol measurements, and clinically meaningful outcomes. Greater attention should also be given to dose-response relationships, food matrix effects, gut microbiota interactions, genetic variability in sterol transporters, and identification of populations most likely to benefit.

CONCLUSION

Advances in food technology, delivery systems, and nutraceutical formulation may further improve phytosterol bioavailability, stability, and functional efficacy while preserving safety. By linking mechanistic insights with translational and clinical research, future studies can support more precise and personalized nutrition strategies. Overall, phytosterols remain a compelling example of multifunctional dietary bioactives with established cardiometabolic value and promising, though still evolving, applications beyond lipid lowering.