Fatty liver disease affects approximately one in three UK adults, yet many remain unaware of their condition until routine testing reveals it. When diagnosed, patients often wonder whether their liver condition might explain digestive symptoms such as diarrhoea. Understanding the relationship between fatty liver disease and bowel function is important for appropriate management and peace of mind. Whilst uncomplicated fatty liver disease does not directly cause diarrhoea, several indirect mechanisms and coexisting conditions may explain altered bowel habits in affected individuals. This article examines the evidence, explores alternative causes, and provides guidance on when to seek medical advice.

Understanding Fatty Liver Disease and Digestive Symptoms

Fatty liver disease, medically termed hepatic steatosis, occurs when excess fat accumulates in liver cells. The condition exists in two main forms: non-alcoholic fatty liver disease (NAFLD), which affects people who drink little or no alcohol, and alcohol-related fatty liver disease (AFLD). NAFLD is increasingly common in the UK, affecting approximately one in three adults according to NHS estimates, often associated with obesity, type 2 diabetes, and metabolic syndrome.

The liver performs over 500 vital functions, including producing bile for fat digestion, processing nutrients from food, and filtering toxins from the blood. When fat accumulates in liver tissue, it can interfere with these normal functions, though many people with fatty liver disease experience no symptoms initially. This is why the condition is often discovered incidentally during routine blood tests or imaging for other health concerns.

Digestive symptoms can occur in people with fatty liver disease, though the relationship is complex. The liver's role in bile production is particularly relevant—bile acids help emulsify dietary fats in the small intestine, facilitating their absorption. In advanced liver disease, bile composition and flow may be altered, potentially affecting digestive processes. Additionally, fatty liver disease frequently coexists with other metabolic conditions that can independently influence bowel function.

It's important to understand that fatty liver disease exists on a spectrum. Simple steatosis (fat accumulation alone) carries a lower risk of progression than NASH, but requires ongoing risk assessment per NICE guidance (NG49). Non-alcoholic steatohepatitis (NASH) involves inflammation and liver cell damage, which can progress to fibrosis and cirrhosis. The presence and severity of digestive symptoms may vary depending on disease stage and individual factors.

Can Fatty Liver Cause Diarrhoea?

There is no direct, established causal link between uncomplicated fatty liver disease and diarrhoea. Simple hepatic steatosis does not typically cause diarrhoea as a primary symptom, as confirmed by NICE guidance (NG49) and British Society of Gastroenterology (BSG) literature. Most people with fatty liver disease remain asymptomatic or experience only vague symptoms such as fatigue or mild right upper quadrant discomfort. Diarrhoea is not listed among the characteristic features of NAFLD.

However, several indirect mechanisms may explain why some individuals with fatty liver experience altered bowel habits:

• Bile acid diarrhoea: The liver produces bile acids essential for fat digestion. Bile acid diarrhoea (also called bile acid malabsorption) typically causes chronic watery diarrhoea rather than fatty stools. This condition can occur when bile acids are not properly reabsorbed in the small intestine and reach the colon, where they stimulate water secretion. Testing via SeHCAT scan or serum 7α-hydroxy-4-cholesten-3-one (7αC4) may be considered by specialists per BSG guidance. This is distinct from steatorrhoea (fatty, pale, offensive stools), which occurs with cholestasis or pancreatic insufficiency.

• Advanced liver disease: When fatty liver progresses to cirrhosis, portal hypertension and altered gut motility can develop. Small intestinal bacterial overgrowth (SIBO) becomes more common in advanced liver disease and can cause diarrhoea. These complications occur in advanced disease, not simple steatosis.

• Medication effects: Treatments for conditions associated with fatty liver commonly cause diarrhoea as a side effect. Metformin, used for type 2 diabetes, causes gastrointestinal side effects including diarrhoea in a significant proportion of users (reported incidence varies; consult the BNF or medicine's Summary of Product Characteristics). Modified-release formulations may be better tolerated.

If you have fatty liver disease and experience persistent diarrhoea, it's more likely that another concurrent condition is responsible rather than the fatty liver itself. The metabolic syndrome that often accompanies NAFLD includes insulin resistance, which may influence gut motility and the gut microbiome. Additionally, dietary changes people make after a fatty liver diagnosis—such as increasing fibre intake or reducing fat consumption—can temporarily alter bowel habits.

Other Causes of Diarrhoea in People with Fatty Liver

People with fatty liver disease may experience diarrhoea due to various coexisting conditions or lifestyle factors. Understanding these alternative explanations is important for appropriate management.

Metabolic and endocrine conditions frequently overlap with fatty liver disease. Type 2 diabetes affects gut motility through autonomic neuropathy and is often treated with metformin, which causes diarrhoea in a significant proportion of users (see BNF for full adverse effect profile). GLP-1 receptor agonists (such as semaglutide or liraglutide), increasingly used for weight management and diabetes in people with NAFLD, can also cause gastrointestinal side effects including diarrhoea. Thyroid disorders, particularly hyperthyroidism, can accelerate gut transit and cause frequent loose stools whilst also being associated with metabolic dysfunction.

Dietary factors play a significant role. Many individuals diagnosed with fatty liver make substantial dietary changes, including:

• Dramatically increasing fibre intake, which can cause temporary digestive upset if introduced too rapidly

• Consuming artificial sweeteners (sorbitol, xylitol) in 'sugar-free' products, which have laxative effects

• Increasing coffee consumption, a natural gut stimulant

• Eliminating or severely restricting dietary fat

• Using orlistat (a lipase inhibitor for weight loss), which commonly causes oily stools and diarrhoea

Gastrointestinal conditions such as irritable bowel syndrome (IBS), coeliac disease, inflammatory bowel disease (IBD), and microscopic colitis can occur independently of liver status. An association between coeliac disease and NAFLD has been reported; consider testing where appropriate per NICE guidance (NG20). Faecal calprotectin testing (NICE DG11) can help distinguish IBS from IBD in primary care when evaluating persistent diarrhoea.

Medications beyond diabetes treatments can contribute to diarrhoea. Statins, commonly prescribed for dyslipidaemia in people with fatty liver, occasionally cause digestive disturbance (see BNF). Proton pump inhibitors (PPIs), widely used for reflux symptoms, have been associated with an increased risk of Clostridioides difficile infection and may alter gut bacteria.

Small intestinal bacterial overgrowth (SIBO) has been reported more frequently in people with NAFLD in some studies, possibly due to altered gut motility and changes in the gut-liver axis. SIBO can cause chronic diarrhoea, bloating, and malabsorption.

If you suspect a medicine is causing diarrhoea, discuss this with your GP or pharmacist. You can report suspected side effects via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app. Never stop prescribed medications without medical advice.

When to See Your GP About Liver and Bowel Symptoms

Whilst fatty liver disease itself rarely causes diarrhoea, certain combinations of symptoms warrant prompt medical evaluation. You should contact your GP if you experience:

• Persistent diarrhoea lasting more than two weeks

• Blood in your stools or black, tarry stools (melaena)

• Unintentional weight loss accompanying bowel changes

• Severe abdominal pain or persistent vomiting

• Signs of dehydration (dizziness, reduced urination, extreme thirst)

• Nocturnal diarrhoea that wakes you from sleep

• Change in bowel habit (particularly if aged 50 or over)—see NICE guidance (NG12) on suspected cancer recognition and referral

Seek urgent medical attention if you develop symptoms suggesting advanced liver disease or complications:

• Yellowing of the skin or eyes (jaundice)

• Swelling of the abdomen (ascites) or ankles

• Confusion or altered mental state (hepatic encephalopathy)

• Vomiting blood or passing very dark stools (possible variceal bleeding)

• Severe, persistent abdominal pain

Your GP will take a thorough history, including the nature and frequency of diarrhoea, associated symptoms, dietary changes, and current medications. Physical examination may include abdominal palpation to assess liver size and tenderness. Investigations may include:

• Blood tests: full blood count, liver function tests, coeliac serology (per NICE NG20 if appropriate), thyroid function, inflammatory markers, and glucose/HbA1c

• Stool samples: to exclude infection, inflammation (faecal calprotectin per NICE DG11), or malabsorption

• NAFLD risk stratification: if not recently performed, your GP may calculate a FIB-4 score or NAFLD Fibrosis Score to assess the risk of advanced liver fibrosis. If intermediate or high risk, an Enhanced Liver Fibrosis (ELF) blood test may be arranged, or referral to a specialist for further assessment (per NICE NG49)

• Further imaging: ultrasound if liver status unclear; transient elastography (FibroScan) is typically arranged by liver specialists to assess fibrosis

For people with known fatty liver disease, regular monitoring is important. NICE recommends that individuals with NAFLD should have periodic assessment of liver fibrosis risk using non-invasive tests such as FIB-4 or the NAFLD Fibrosis Score. If you develop new digestive symptoms between scheduled reviews, don't wait—contact your GP to ensure nothing significant is being missed. Early identification of progressive liver disease or alternative diagnoses ensures timely, appropriate management.

Managing Digestive Health with Fatty Liver Disease

Effective management of fatty liver disease centres on lifestyle modification, which simultaneously benefits both liver and digestive health. A holistic approach addresses the underlying metabolic dysfunction whilst supporting optimal gastrointestinal function.

Dietary strategies form the cornerstone of management. NICE guidance (NG49) recommends:

• Gradual weight loss of 5–10% of body weight for those who are overweight, which can significantly reduce liver fat and improve insulin sensitivity

• Mediterranean-style diet rich in vegetables, fruits, whole grains, legumes, nuts, and olive oil, with moderate fish consumption

• Reducing refined carbohydrates and added sugars, particularly fructose-containing beverages

• Adequate fibre intake (30 g daily per NHS guidance), introduced gradually to avoid digestive upset—soluble fibre from oats, beans, and vegetables is particularly beneficial

• Regular meal patterns to support stable blood glucose and healthy gut motility

Physical activity benefits both liver and bowel function. The UK Chief Medical Officers recommend at least 150 minutes of moderate-intensity activity weekly (or 75 minutes vigorous activity). Exercise improves insulin sensitivity, reduces liver fat, and promotes regular bowel movements through enhanced gut motility.

Managing medications requires careful consideration. If you suspect a medication is causing diarrhoea, discuss alternatives with your GP—never stop prescribed medications without medical advice. For metformin-related diarrhoea, modified-release formulations or gradual dose titration may help (consult BNF or medicine's Summary of Product Characteristics). Report suspected side effects via the MHRA Yellow Card scheme.

Gut health optimisation includes:

• Staying well hydrated (approximately 1.6–2 litres daily for most adults)

• Considering probiotic-rich foods (live yoghurt, kefir, fermented vegetables)—note that evidence for probiotics in NAFLD and diarrhoea is mixed and they are not a substitute for prescribed management

• Limiting alcohol: follow UK Chief Medical Officers' guidance of no more than 14 units weekly, spread over three or more days, with several alcohol-free days. If you have advanced fibrosis or cirrhosis, abstinence is advised

• Managing stress, which may influence symptoms and health behaviours

Monitoring and follow-up ensure your management plan remains effective. Keep a symptom diary noting bowel habits, dietary intake, and any triggers. This information helps your healthcare team identify patterns and adjust your treatment accordingly. Remember that improving fatty liver disease is a gradual process—sustainable lifestyle changes yield better long-term outcomes than rapid, unsustainable interventions.

Frequently Asked Questions