Medically reviewed guide · Last updated: 19 November 2026 · Reading time: approx. 11 min

Fatty Stools: Pancreas, Coeliac Disease or Medication?

The most common causes compared

The causes in detail

Fat is the most demanding part of our food: bile first has to break it down into fine droplets, enzymes from the pancreas (above all lipase) have to split it, and a healthy lining of the small intestine has to absorb the building blocks. If any of these steps fails, the fat arrives undigested in the large intestine. Fatty stools are therefore not a condition in their own right, but a sign of a problem with fat digestion (malabsorption). Not every soft or frequent stool is a fatty stool — watery, urgent stools are covered in the article on diarrhoea, and colour changes due to a lack of bile in the article on pale stool.

A weak pancreas: the most common reason

In exocrine pancreatic insufficiency, the pancreas produces too few digestive enzymes. Fatty stools usually only appear once most of the enzyme capacity has been lost — by then the condition has often been present for some time. Typical triggers are chronic pancreatitis (often due to alcohol and smoking), cystic fibrosis, operations on the pancreas or stomach and long-standing diabetes. A tumour can also block the pancreatic duct. Fatty stools are often accompanied by bloating, abdominal pain after eating and weight loss. First step: measuring pancreatic elastase in the stool and an ultrasound of the upper abdomen.

Coeliac disease: when the gut lining does not cooperate

In coeliac disease, gluten from wheat, rye, barley and spelt triggers inflammation of the lining of the small intestine. The villi, through which nutrients are absorbed, waste away. Besides fatty stools, bloating, tiredness, iron deficiency, bone loss and an intensely itchy blistering rash (dermatitis herpetiformis) are typical — but many people affected only have non-specific symptoms. First step: an antibody blood test while you are still eating a normal diet containing gluten. Cutting out gluten beforehand distorts the tests.

Missing bile: bile blockage and bile acid loss

Without bile, fat is not dissolved. If a gallstone, a narrowing or a tumour blocks the bile duct, the stool becomes pale and greasy, the urine dark, and jaundice follows. Advanced liver diseases such as liver cirrhosis have a similar effect. Another route: bile acids are normally reabsorbed in the last section of the small intestine. If this section is inflamed in Crohn’s disease or a longer piece has been removed, bile is lost — the result is diarrhoea and, with greater losses, fatty stools as well. First step: liver values and ultrasound, promptly if there is jaundice.

Infections and bacterial overgrowth in the small intestine

Giardia (Giardia lamblia), intestinal parasites from contaminated water, temporarily damage the lining of the small intestine and cause foul-smelling, greasy diarrhoea with bloating — typically after long-distance travel. In small intestinal bacterial overgrowth, for example after gastrointestinal surgery, with narrowings or slowed bowel movement, bacteria break down the bile acids before they can work. Rare causes are Whipple’s disease and short bowel syndrome after major surgery. First step: a stool test; with bacterial overgrowth, breath tests can provide clues.

Harmless: food and certain fish

Eating a very large amount of fat at once can lead to a one-off greasier stool. A special case is escolar (sold in Germany as Buttermakrele) and so-called oilfish: they contain wax esters that the body cannot digest. A few hours after eating, an orange, oily discharge occurs, often without warning. This is unpleasant but harmless and stops after one to two days. What matters: a single greasy stool after a particular meal is not a sign of illness; recurring fatty stools over weeks are.

When a tumour needs to be considered

To put it honestly: most cases of fatty stools have benign causes. Pancreatic cancer can, however, show up in exactly this way — especially if, from middle age onwards, fatty stools, unintentional weight loss, back pain, painless jaundice or newly diagnosed diabetes occur together. Then the investigation should not be put off but should happen within the next few days.

Self-tests: first clues at home

These observations do not replace a stool or blood test or a diagnosis. But they help you tell fatty stools apart from other changes in the stool and prepare for the conversation.

• The toilet test: is the stool shiny, does it leave an oily film or droplets of fat on the water, does it stick to the bowl and is it hard to flush away? That points to fat. Floating stool on its own, on the other hand, is not a reliable sign — it often simply contains a lot of gas.
• The meal test: for one week, note down what you eat and what the stool looks like. If it gets clearly worse after fatty meals, that fits with missing enzymes or orlistat; after bread and pasta, think more of coeliac disease — but do not cut out gluten before the test.
• The scales test: weigh yourself once a week at the same time. Losing weight without trying while your appetite is normal is an important sign that nutrients are being lost.
• The accompanying signs check: dark urine or yellowish eyes? New bruises or bleeding gums (vitamin K deficiency)? Poor vision at dusk (vitamin A deficiency)? A lot of thirst or frequent urination?
• The look-back check: do you take orlistat, a bile acid sequestrant or injections for hormone-producing tumours? Have you travelled in the last few weeks? How much alcohol do you drink per week, honestly counted?

Warning signs: when not to wait

• Fatty stools with jaundice, dark urine or severe itching
• Severe upper abdominal pain that radiates around like a band into the back, often with nausea and vomiting
• Blood in the stool or black stool
• Fever, severe diarrhoea with dizziness, passing little urine or signs of dehydration
• Unintentional weight loss, especially together with newly diagnosed diabetes
• A noticeable tendency to bleed, for example many bruises or long-lasting nosebleeds
• Greasy stools and poor growth in a child

The treatment pathway: step by step

1. Observe and take notes. A single greasy stool after a rich meal or fish: wait and see. Recurring over two to three weeks: note down your stools, meals, weight and medicines and make an appointment.
2. GP practice. A conversation about what your stools look like, your weight, alcohol, travel, operations and all your medicines, plus an examination of the abdomen.
3. Laboratory tests. Full blood count, liver and bile values, lipase, blood sugar and HbA1c, coeliac antibodies including total IgA, iron, vitamin D and clotting as an indication of vitamin K deficiency. What the values mean is explained in the guide Understanding blood values.
4. Stool test. Pancreatic elastase in the stool shows whether the pancreas is producing enough enzymes; with very watery stools, the test is less reliable. In addition, pathogens such as Giardia. Measuring fat in stool collected over several days is rarely needed nowadays.
5. Imaging and endoscopy. Ultrasound of the upper abdomen and, depending on the findings, endoscopic ultrasound, CT or MRI. If coeliac disease is suspected, a gastroscopy with tissue samples from the duodenum confirms the diagnosis.
6. Treatment according to the cause. With enzyme deficiency, pancreatic enzymes with every meal; with coeliac disease, a lifelong gluten-free diet; bile duct and liver diseases are treated specifically, Giardia with an antiparasitic medicine. Missing vitamins are replaced. Which treatment suits you is always decided by the practice treating you.

The medication angle: triggers, treatment and interactions

With fatty stools, medicines play a double role: some trigger them, others are the most important treatment — and taking them correctly determines whether they work.

Orlistat: fatty stools as the mode of action

The weight-loss active substance orlistat, available both over the counter and on prescription, inhibits lipase in the gut so that part of the dietary fat is excreted undigested. According to the summary of product characteristics, oily spotting, urgency, oily discharge with wind and fatty stools are very common, especially after fatty meals. Orlistat also reduces the absorption of fat-soluble vitamins; a multivitamin taken at a different time, for example at bedtime, is therefore recommended. The interactions are important: the summary of product characteristics lists, among others, ciclosporin, levothyroxine, antiepileptic medicines, amiodarone and anticoagulants such as phenprocoumon. With severe diarrhoea, the pill can become unreliable. For an overview of other weight-loss medicines, see the guide Weight-loss injections compared.

Other possible triggers

Bile acid sequestrants such as colestyramine, which are used for high blood lipids or bile acid diarrhoea, can encourage fatty stools at higher doses and interfere with the absorption of fat-soluble vitamins and other medicines. Somatostatin analogues such as octreotide, used for example for hormone-producing tumours, slow down the pancreas — fatty stools are a known side effect. Metformin and GLP-1 receptor agonists such as semaglutide often cause soft stools and diarrhoea, but generally not true fatty stools; with GLP-1 receptor agonists, you should also watch out for signs of an inflamed pancreas. Alcohol is not a medicine, but it is the most important avoidable factor for chronic pancreatitis.

Pancreatic enzymes: taking them correctly

With enzyme deficiency, capsules containing pancreatin replace the missing enzymes. They only work if they reach the gut together with the food: at the start of or during every meal and every snack containing fat, not afterwards on an empty stomach. The dose depends on the fat content of the meal and is set and adjusted by the practice. Do not chew the capsules; if you have trouble swallowing, the package leaflet has advice. If the effect is not sufficient, the practice can also prescribe an acid blocker such as pantoprazole. More on the right timing in the guide Medications before or after eating.

Vitamins and painkillers

Missing vitamins A, D, E and K are replaced according to laboratory values, often including vitamin D and calcium to protect against osteoporosis. Do not take high-dose vitamins on your own initiative — vitamins A and D in particular can be overdosed. With abdominal pain due to chronic pancreatitis, pain treatment belongs in medical hands; over-the-counter painkillers should not be taken for longer than three to four days in a row or on more than ten days a month without medical advice. Anti-diarrhoeal medicines such as loperamide only treat the symptom and mask the cause.

How to prevent fatty stools and their consequences

• Cut down on alcohol and smoking — both are the most important avoidable causes of chronic pancreatitis and make an existing weakness of the pancreas progress.
• Limit fat while taking orlistat — evenly spread meals with a moderate fat content clearly reduce the side effects on the gut.
• Watch the water when travelling — boiled or bottled water protects against Giardia and other gut pathogens.
• Have vitamins and bones checked — with known malabsorption, check vitamin levels regularly and bone density if needed.
• Record supplements — vitamins, calcium and enzymes belong in your medication plan; more on this in the guide Supplements and medications.

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