Does Fatty Liver Cause Smelly Poop?

Fatty liver disease and smelly poop are not often discussed together, yet the liver's role in bile production means that hepatic steatosis can indirectly influence stool odour and consistency. When fat accumulates in liver cells, bile acid metabolism may be disrupted, affecting how dietary fats are digested in the gut. This article explains the mechanisms behind these changes, what other symptoms may accompany them, when to seek medical advice, and which lifestyle changes are most effective for improving both liver health and digestive function.

Can fatty liver disease really affect the smell of your poo?

Fatty liver disease can indirectly alter stool odour by disrupting bile acid metabolism, leading to incomplete fat digestion and bacterial fermentation, though smelly stools alone are not a reliable indicator of the condition.

Fatty liver disease can contribute to changes in stool odour, though it is rarely the sole cause and the link is indirect. The liver produces bile, a fluid that helps break down dietary fats in the small intestine.^[1] When excess fat accumulates in liver cells, a condition known medically as hepatic steatosis, bile acid metabolism can be affected.^[15][16] This is most relevant in more advanced disease or where there is associated cholestasis; in early, uncomplicated metabolic dysfunction-associated steatotic liver disease (MASLD), significant changes to bile flow are not typical.

In more advanced stages, such as metabolic dysfunction-associated steatohepatitis (MASH, formerly called NASH), liver inflammation can further disrupt bile acid metabolism.^[15][16] When fats pass through the gut incompletely digested, colonic bacteria ferment them, producing gases and short-chain fatty acids that can alter stool smell. Stool odour is also influenced by protein fermentation and changes in bile acid composition, so the mechanism is not straightforward.

It is important to note that smelly stools alone are not a reliable indicator of fatty liver disease. Many other factors, including diet, gut infections, lactose intolerance, coeliac disease, and the use of certain medicines, can produce similar changes. MASLD is most commonly associated with obesity, type 2 diabetes, high triglycerides, and high cholesterol.^[2][13] Alcohol-related liver disease (ARLD) is a separate condition with overlapping features but a different cause. If you have known risk factors and are also noticing persistent digestive changes, it is worth discussing both with your GP rather than attributing the symptoms to a single cause.

How does a fatty liver change the way your gut works?

Fatty liver disease alters gut function via changes in bile acid composition, gut microbiome balance, and intestinal permeability, with the gut-liver axis meaning bacterial products from the gut can worsen liver inflammation.

Fatty liver disease can alter gut function through its effect on bile acid metabolism, gut microbiome composition, and intestinal permeability, though the extent of these changes varies with disease severity. Bile acids produced by the liver help regulate the balance of bacteria in the small intestine. When bile acid composition changes, particularly in more advanced liver disease, this balance can be disrupted, potentially contributing to bloating, excess gas, and altered stool consistency.

Research has identified a bidirectional relationship between the liver and the gut, often referred to as the gut-liver axis. The liver receives blood directly from the intestines via the portal vein, meaning that substances produced by gut bacteria, including bacterial toxins, travel straight to the liver.^[12][14] In people with fatty liver disease, increased intestinal permeability (a state in which the gut lining becomes more permeable than normal) may allow more of these bacterial products to reach the liver, worsening inflammation and potentially contributing to disease progression.^[12][13]

Pale, greasy, or floating stools, a condition known as steatorrhoea, can occur when fat is not properly absorbed. It is worth noting that steatorrhoea is not a typical feature of isolated MASLD; when present, it more commonly suggests cholestasis, biliary obstruction, pancreatic insufficiency, or coeliac disease, and warrants prompt medical review.^[6] These stools tend to be particularly malodorous because of undigested fat and fermentation by colonic bacteria. Some people with liver disease also report changes in bowel habit, though the mechanisms are not fully established. Understanding these connections helps explain why digestive symptoms and liver health can be closely linked.

What other symptoms often appear alongside digestive changes?

Fatigue, upper right abdominal discomfort, bloating, and elevated liver enzymes are common alongside digestive changes; jaundice, ascites, or confusion indicate advanced disease requiring urgent assessment.

Fatty liver disease frequently presents with a cluster of symptoms beyond digestive changes, many of which reflect the liver's broader role in metabolism. Fatigue is one of the most commonly reported symptoms, often described as a persistent tiredness that does not improve with rest. The precise cause is not fully understood but is thought to relate to metabolic changes associated with liver disease.

Abdominal discomfort, particularly a dull ache or feeling of fullness in the upper right side of the abdomen, is another common feature. This area corresponds to the location of the liver beneath the ribcage, and mild enlargement of the liver (hepatomegaly) can cause this sensation. Some people also notice:

• Bloating and excess wind, often related to gut microbiome changes

• Nausea, particularly after eating fatty meals

• Elevated liver enzymes (ALT and AST) found incidentally on blood tests

In more advanced disease, symptoms such as jaundice (yellowing of the skin or whites of the eyes), dark urine, significant swelling of the abdomen (ascites), or easy bruising may develop. These suggest progression towards cirrhosis or liver failure and require prompt medical assessment. Cognitive difficulties such as confusion or difficulty concentrating are features of hepatic encephalopathy, which occurs in advanced liver disease, and are not typical of early MASLD.

It is worth noting that many people with early fatty liver disease have no symptoms at all, and the condition is often discovered during routine blood tests or an ultrasound scan performed for another reason. This is why awareness of risk factors is particularly important.

When should you see a GP about smelly or unusual stools?

See your GP if stool changes persist beyond two to three weeks, or immediately if you notice pale greasy stools, blood, jaundice, or unexplained weight loss, as these may indicate serious underlying conditions.

You should see your GP if changes in stool smell or appearance persist for more than two to three weeks, particularly if they are accompanied by other symptoms that could suggest an underlying condition. Occasional changes in stool odour are normal and often reflect short-term dietary shifts or a mild gut upset. However, certain features warrant prompt medical review.

Contact your GP if you notice any of the following:

• Pale, greasy, or floating stools that are difficult to flush away (possible steatorrhoea, which may suggest cholestasis, pancreatic insufficiency, or coeliac disease rather than fatty liver alone)^[6]

• Persistent diarrhoea or constipation lasting more than a few weeks

• Blood in your stools or black, tarry stools (contact your GP urgently or call NHS 111 for same-day advice)

• Unexplained weight loss alongside digestive changes

• Yellowing of the skin or eyes (jaundice), which requires same-day assessment via NHS 111 or your GP

• Significant abdominal pain or swelling

If you have known risk factors for fatty liver disease, such as obesity, type 2 diabetes, high triglycerides, or a history of heavy alcohol use, your GP may arrange blood tests to check liver function (including ALT, AST, and GGT), a fasting lipid profile, and blood glucose. In UK primary care, the FIB-4 score (calculated from age, ALT, AST, and platelet count) is used as a first-line, non-invasive tool to assess the risk of significant liver fibrosis, in line with NICE and BSG guidance. A liver ultrasound is the most commonly used first-line imaging investigation and can detect fatty changes in the liver. Where FIB-4 or other markers suggest a higher risk of fibrosis, further assessment with the enhanced liver fibrosis (ELF) score or transient elastography (FibroScan) may be arranged, and referral to hepatology is considered where results suggest advanced fibrosis or cirrhosis.^[4][5] Early identification allows lifestyle interventions to be started before significant liver damage occurs.

Lifestyle changes that can improve both liver health and digestion

Gradual weight loss of 7 to 10 per cent of body weight, a Mediterranean-style diet, reduced alcohol intake, and at least 150 minutes of weekly aerobic activity are the most evidence-based approaches for improving MASLD and digestive symptoms.

Gradual, sustained weight loss is the most evidence-based intervention for improving fatty liver disease and, in turn, digestive symptoms including stool changes. NICE guidance (NG49) recommends aiming for a loss of around 7 to 10 per cent of body weight in people with MASLD, as this level of reduction has been shown to reduce liver fat, lower inflammation, and improve liver enzyme levels.^[2] Unsupervised crash dieting is not advisable, as rapid weight loss without medical oversight can worsen liver inflammation; however, supervised very-low-calorie programmes may be appropriate in some cases and should be discussed with a clinician.^[6]

Dietary changes that support both liver health and gut function include:

• Reducing intake of ultra-processed foods, added sugars, and saturated fats, which contribute to liver fat accumulation

• Increasing dietary fibre from vegetables, legumes, wholegrains, and fruit to support a healthy gut microbiome

• Following a Mediterranean-style eating pattern, which has evidence for reducing liver fat and improving metabolic markers^[10][11]

• Limiting or avoiding alcohol, which is directly toxic to liver cells regardless of the underlying cause of fatty liver

• Staying well hydrated to support bowel regularity

Regular physical activity, including both aerobic exercise and resistance training, independently reduces liver fat even without significant weight loss.^[18][19] UK Chief Medical Officers' guidelines recommend at least 150 minutes of moderate-intensity aerobic activity per week for adults, alongside muscle-strengthening activities on at least two days per week. Managing conditions such as type 2 diabetes and high cholesterol through medication and lifestyle also reduces the metabolic burden on the liver.

For people seeking structured support with weight management, Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online weight-management consultations, with prescriber review and pharmacist support. Any treatment is only recommended where it is clinically appropriate following a full assessment. Suspected side effects from any medicine can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

Scientific References

1. Fat digestion and absorption: Normal physiology.
2. Metabolic dysfunction-associated steatotic liver disease (NG49).
3. Alcoholic fatty liver disease [DAP59] – Protocol.
4. FibroScan for assessing liver fibrosis and cirrhosis outside secondary and specialist care (DG48).
5. FibroScan for assessing liver fibrosis and cirrhosis in primary care (HTG682) – Consultation document.
6. Non-alcoholic fatty liver disease (NAFLD).
7. Physical activity guidelines for adults aged 19 to 64.
8. Physical activity guidelines: UK Chief Medical Officers' report.
9. UK Chief Medical Officers' physical activity guidelines.
10. Mediterranean diet for the management of metabolic dysfunction-associated steatotic liver disease.
11. The Metabolic and Hepatic Impact of Two Personalized Dietary Strategies in Subjects with Obesity and Nonalcoholic Fatty Liver Disease: The FLiO Randomized Controlled Trial.
12. The gut-liver axis: microbial mechanisms and therapeutic implications in MAFLD.
13. MASLD beyond the liver: decoding the gut-genetic-metabolic nexus.
14. The liver-gut-brain axis in metabolic dysfunction-associated steatotic liver disease: bidirectional communication, clinical implications, and future perspectives.
15. EASL position paper on preclinical models of steatotic liver disease.
16. Current Update on Nomenclature, Diagnosis, and Management of Metabolic Dysfunction-associated Steatotic Liver Disease: Radiologists' Perspective.
17. Metabolic dysfunction and alcohol-related liver disease (MetALD): Position statement by an expert panel on alcohol-related liver disease.
18. Structured Exercise Interventions and Hepatic-Metabolic Outcomes in Adults with MASLD: A Narrative Review of Randomized Controlled Trials.
19. The Effects of a Short-Term Combined Exercise Program on Liver Steatosis Indices and the Lipidemic and Glycemic Profile in NAFLD Individuals: A Pilot Study.

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