April 21, 2026

Fatty Liver Disease, MASLD, and SIBO Fatty liver disease, particularly Nonalcoholic Fatty Liver Disease (NAFLD), now known as Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD), has become a major global health concern. In recent years, MASLD has been the second leading cause of end-stage liver disease worldwide (28). Increasing evidence reveals a fascinating connection between NAFLD and gut health, specifically a condition known as Small Intestinal Bacterial Overgrowth (SIBO). The correlation between small intestinal bacterial overgrowth (SIBO) and nonalcoholic fatty liver disease (NAFLD) has gained heightened acknowledgment, especially in the late phases of liver disease. Today, we explore the scientific links between these two conditions and why understanding this relationship matters. Understanding The Gut-Liver Axis The gut epithelium is a natural barrier that selects entry of useful substances present in the lumen, as nutrients, and keeps at bay bacteria, their bio-products and other potentially harmful elements. Tight junctions, specialized intercellular structures, assist this control. Derangement of the homeostasis between bacteria and the host, as occurs in SIBO (enhanced amount and/or changes in the type of bacteria in the gastrointestinal tract), may cause disruption of the intercellular tight junctions and subsequent increase in intestinal permeability leading to bacterial translocation (BT), i.e., transportation of bacteria and bacterial products from the intestinal lumen into the blood (4). The portal vein and the hepatic artery supply blood to the liver. The portal blood contains products of digestion and microbial products derived from the gut microbiota. This blood is carried to the liver. Therefore, Liver is the first site of exposure and filtration that consists of microbial products from the gut, such as LPS, lipopeptides, unmethylated DNA, and double-stranded RNA, which may evoke inflammatory reaction contributing to the progression of the liver disorder (4). This bidirectional relationship of the gut ecosystem and liver is imperative both physiologically and pathologically. Generally, the liver receives rich nutrients, microbial metabolites, and subproducts from the intestine and secretes bile into the small intestine (5). An integrated gut barrier also protects against toxins to maintain internal homeostasis. This gut-liver axis is regulated and stabilized by a complex network of metabolic, immune, and neurosecretory interactions between the gut, microbiota, and liver. Disruption of this equilibrium may lead to gut dysbiosis and liver injury (5). SIBO as we know is the clinical manifestation of gut microbial dysbiosis. Therefore, the bidirectional relationship between Small Intestinal bacterial overgrowth (SIBO) and fatty liver disease, particularly non-alcoholic fatty liver disease (NAFLD), is characterized by mutual influences through gut-liver axis dysfunction, inflammation, and metabolic disturbances. Association between SIBO and Fatty Liver Small intestinal bacterial overgrowth (SIBO) is a condition marked by excessive growth of microbes in the small intestine, resulting in various digestive issues including bloating, satiety, and malabsorption. In healthy people, the small bowel has a relatively low bacterial concentration, around 103–104 colony-forming units per milliliter (CFU/mL) (1,6). However, when this balance is disrupted, bacteria from the colon or oral cavity can colonize the small intestine, resulting in SIBO. Factors contributing to this condition include reduced gastric acid production, impaired intestinal motility, insufficient production of bile and dysfunction of the ileocecal valve (1,7). It may present in a range of symptoms, from moderate pain to severe nutritional deficiencies, weight loss, and shortages in crucial minerals and vitamins, including vit B12, A, D, E, iron, choline, calcium, fats, carbohydrates, protein and bile salt deconjugation (1,8). However, it has been shown that intestinal dysbiosis, endotoxemia (bacterial toxins in blood) and bacterial translocation may contribute to inflammation and Insulin Resistance (3,9,10,11,12). This directly seems to disrupt the functioning of the gut–liver axis, which may influence the incidence and progression of NAFLD (3,13). Non-alcoholic fatty liver Disease is the most frequent cause of chronic liver sickness globally, with a spectrum spanning from simple steatosis to inflammation of the hepatocytes, fibrosis, cirrhosis, and even hepatocellular carcinoma (1,14). The link between SIBO and nonalcoholic fatty liver disease (NAFLD) has attracted increased attention since studies show that the gut-liver axis plays a significant role in the pathophysiology of steatosis liver disease (1,15). The transfer of bacterial metabolites from the stomach to the liver may promote scarring and inflammation, thereby aggravating liver damage (1,16). How SIBO affects Fatty Liver?   Inflammation – SIBO leads to an overgrowth of bacteria in the small intestine, causing increased intestinal permeability “known as leaky gut or gut barrier dysfunction.” This allows bacterial endotoxins, especially lipopolysaccharides (LPS), to enter the bloodstream and reach the liver via the portal vein, triggering chronic liver inflammation. These endotoxins and bacterial products activate inflammatory pathways (immune responses) in the liver, releasing proinflammatory cytokines (e.g. TNF-α, IL-6) which promote fat accumulation, insulin resistance, liver inflammation, fibrosis, and disease progression in NAFLD. Example – It has been demonstrated in animal models that a four-week HFD (high fat diet) increases LPS contained in the gut microbiota and plasma LPS concentrations two to three times, which is considered metabolic endotoxemia. The induction of metabolic endotoxemia in mice, by continuous subcutaneous infusion of LPS for four weeks, was followed by a rise in the following parameters: fasting glycemia, insulinemia, markers of inflammation, liver triglyceride content, liver insulin resistance, and whole body, liver and adipose tissue weight gain in a similar amount as occurred in HFD fed mice (4,17). Large amount of fructose consumption is also related to increase in endotoxin serum levels, proinflammatory response and steatosis. It was demonstrated in an elegant study conducted by Bergheim et al. (4,18) that mice fed with fructose showed increased endotoxin levels in the portal blood, and higher intrahepatic lipid accumulation, lipid peroxidation and TNF-α expression. Metabolic disruption – SIBO also disrupts bile acid metabolism, nutrient absorption, and adipose tissue function, contributing further to liver fat deposition and dysfunction. Bile acids – Bile acids are synthesized in the liver from cholesterol, conjugated (joined) with glycine or taurine, and secreted into the small intestine, where they help digest fats and maintain gut microbial balance through their antimicrobial properties (3). In a healthy gut, most bile acids are absorbed in the ileum, while the

How Leaky Gut Drives Leaky Brain? This article focuses on the possible neuropsychological basis of leaky gut; leaky brain disease; and the microbiota’s contribution to inflammation, gastrointestinal, and blood-brain barrier (BBB) integrity.  As already indicated, in my other article titled as “leaky gut syndrome,” various diseases have been related to dysbiosis of the intestinal microbiota, microbial translocation, and dysfunction of the intestine’s barrier function. Among them, we can highlight IBS, IBD, Obesity, Chronic Heart Failure, Autism, Alzheimer’s Disease, Cancer, Diabetes, and Autoimmune Diseases like Type 1 Diabetes and Celiac Disease (1). Critical to any discussion on leaky barrier systems are pathogens, which, unlike commensals, have evolved elaborated mechanisms to target host barrier integrity and disseminate systemically to invade deeper tissues and organs. This pathogen gains entry into the blood stream by acting through type IV pili on bacterial surfaces, interacting with molecules on endothelial cells to disrupt the tight junctions and occasionally escape the mucosal barrier to enter the bloodstream and pass into the meninges of the brain and its surrounding membranes to cause disease and breach the blood–brain barrier (BBB) (1,4). To understand a possible connection between leaky gut and possible leaky brain, let’s examine the barriers involved in physiological conditions.  Vital organs and biologic systems have developed barriers to host’s tissues from infection. The notable barriers are the blood brain barrier (BBB), gastrointestinal blood barrier (GBB), blood ocular and blood retinal barriers, blood placenta and blood testis barriers, the blood thymus barrier, and the blood–lung or airway barrier. Each of these barriers protects vulnerable and sensitive organs and systems (1). A key component for the brain is the neurovasculature, which limits blood brain barrier (BBB) permeability and prevents transport of large molecules, many small molecules, and bacteria from entering the brain. Inflammation disrupts BBB and appears to be central to brain and blood brain barrier (BBB) involvement (1).  Many diseases and physiological stressors that affect the Central Nervous System (CNS) also alter the functional integrity of the BBB (9,10). They affect the barrier’s ability to selectively restrict passage of substances from the blood to the brain. To add to this, hypoxia (lack of oxygen supply) and/or inflammation and inflammatory process alter the permeability properties and contribute to the pathophysiology of CNS diseases, leading to altered delivery of therapeutic agents to the brain (5). Selective permeability is important and accomplished through tight junctions, composed of endothelial cells and smaller subunits anchored into the endothelium together with transmembrane proteins, such as junctional adhesion molecule, occludins, adherens, and claudins, for example. The junctional proteins in the brain are like those of the small intestine (1). Tight junctions help protect the brain from toxins, chemicals, and pathogens that might be circulating in the bloodstream. Together with selective transport proteins, the barriers allow nutrients, oxygen, amino acids, some drugs, and glucose to enter the cerebrospinal fluid and prevent hydrophobic molecules from passing into the interfaces of blood–cerebrospinal fluid barriers, namely CSF and choroid plexus. At the same time, it allows the diffusion of many small polar molecules, dissolved gasses, hormones, and hydrophilic molecules (1). In the gut, the barrier between the body and a lumenal environment is formed by gastrointestinal mucosa, buffering nutrients, microorganisms, and toxins. The barriers are semipermeable, thus allowing efficient transport of nutrients across the epithelium, while excluding entry of potentially harmful small molecules and organisms. The exclusionary properties of the gastric and intestinal mucosa are referred to as the gastrointestinal blood barrier (GBB) (1,6). As the barriers share common proteins and features, there is no doubt they may be susceptible to similar mechanisms of compromise or breach, either biochemically or physically. This fact underlies one basis for a plausible LEAKY GUT LEAKY BRAIN SYNDROME. A functional blood–brain barrier is essential to maintaining central nervous system (CNS) homeostasis. BBB weakening may be a result of a disturbance in the endothelial cells due to P-glycoprotein dysfunction (7). If toxins or microorganisms breach the epithelium, they have unrestricted access to the systemic circulation. In the brain, this can occur with disruption of endothelial cells and astrocytes and involve inflammation (8). In the gut, the alimentary canal is lined by epithelial cells that form the mucosa and, with few exceptions, the gastrointestinal epithelium is tied contiguously through tight junctions, where diversity among epithelial cells affect specific barrier functions.  When the Gut-Blood-Barrier (GBB) is breached, there are differences in localization of bacterial species. When a breach occurs, commensal bacteria deposit in the lymphatics and are not found in the blood stream, but species like Salmonella, which by definition are pathogenic – can establish infections in the blood, liver, or other organs. We have evolved with commensals and not pathogens through colonization resistance and other mechanisms, which is one reason why commensal bacteria end up in the nearby lymph nodes and are not found in distal organs despite being proximal to the epithelial linings. Other stressors, such as glycoxidative stress (AGEs), diabetes, prolonged hyperglycemia, and obesity, are risk factors for gut–blood barrier disruption. To resolve these processes, restoration of epithelium (repair of gut lining) must happen, which can be rapid and is accomplished by a process called restitution. Advanced glycation end-products (AGEs) and crosslinking in diabetic complications and with aging may also be a mechanism for barrier protein damage with advanced age (11) and could be mediated through glycotoxins from food. Google definition of Glycotoxins – are compounds, most commonly Advanced Glycation End-products (AGEs), that form when sugars react with proteins or fats. High levels of glycotoxins are linked to oxidative stress, inflammation, and chronic diseases like diabetes, heart disease, and Alzheimer’s. Brain Disorders and Gut Microbiota A dysfunction of the blood brain barrier leading to a ‘leaky brain’ can be linked to various neurological diseases, including autistic spectrum disorder (ASD) (12), dementia, Alzheimer’s disease, depression, and schizophrenia (20,13)  A breakdown in the blood brain barrier was observed in patients with major psychiatric illnesses (14) indicating that the blood–brain barrier may become ‘leaky’ in select neurological diseases that have an immunologic component, such as multiple sclerosis (MS) (15,16),