What Causes Fatty Stools (Steatorrhoea)?

Fatty stools — steatorrhoea — means passing more fat than normal in the stool, because fat is not being adequately digested or absorbed in the intestine.

Steatorrhoea is not a disease in itself. It can be the symptom of various diseases of the pancreas, the small intestine, the liver or the bile ducts. The cause needs to be investigated particularly when fatty stools go on for a long time, or come with weight loss or malnutrition.

How do you recognise a fatty stool?

In steatorrhoea the stool may be:

• Paler than normal,
• Bulky,
• Loose or unformed,
• Shiny or greasy in appearance,
• Foul-smelling,
• Leaving an oily film on the surface of the toilet,
• Able to float on water,
• Hard to clean from the toilet.

But a stool that merely floats does not mean steatorrhoea. A stool containing a lot of gas can float too.

Why is fat passed in the stool?

Several stages have to work properly for the fat we eat to be usable by the body.

The pancreas secretes digestive enzymes, chief among them lipase, which break fat down.

Bile, coming from the liver and the bile ducts, helps fat to be digested in the intestine.

The small intestine then absorbs the digested fat into the body.

A disturbance at any of these stages can mean fat is not adequately absorbed and is passed in the stool instead.

Which diseases can cause steatorrhoea?

Diseases of the pancreas

When the pancreas cannot produce enough digestive enzyme, exocrine pancreatic insufficiency can develop.

Its causes include:

• Chronic pancreatitis,
• Certain operations on the pancreas,
• Obstruction of the pancreatic duct,
• Advanced pancreatic disease.

Steatorrhoea arising from the pancreas can also bring weight loss and deficiencies of certain vitamins.

Diseases of the small intestine

Steatorrhoea can occur if fat is not adequately absorbed from the small intestine even when it has been digested.

Some of the important causes are:

• Coeliac disease
• Certain types of Crohn’s disease
• Surgical removal of a large part of the small intestine
• Certain malabsorption syndromes

Diseases of the bile ducts and the liver

Bile is needed for fat to be digested. Fat absorption can be impaired in some bile duct obstructions and cholestatic diseases where bile does not reach the intestine in sufficient quantity.

These patients can have other findings as well, such as jaundice, dark urine and pale stools.

Medicines

Some medicines can reduce the absorption of fat from the intestine. The medicines and supplements being taken should therefore be reported to the doctor during the assessment.

Why does steatorrhoea matter?

Long-standing impairment of fat absorption changes more than the appearance of the stool.

In time it can lead to:

• Weight loss,
• Malnutrition,
• Muscle loss,
• Fatigue,
• Deficiencies of the fat-soluble vitamins A, D, E and K.

Persistent fatty stools should not therefore be dismissed as simply a change in bowel habit.

How is the diagnosis made?

The first things assessed are the characteristics of the stool, how long the complaint has been present, weight loss, eating habits, the medicines being taken and any accompanying diseases.

Where it is thought necessary, investigations such as the following may be used:

• Blood tests,
• Assessment of vitamin and nutritional status,
• Faecal fat studies,
• Faecal elastase,
• Blood tests for coeliac disease,
• Ultrasound,
• CT or MRI,
• Endoscopy,
• Endoscopic ultrasound (EUS).

Not every patient needs all of these tests. The investigations are chosen according to the cause being considered.

What is the faecal elastase test?

Faecal elastase is a test measured in a stool sample that tells you about the pancreas’s capacity to produce digestive enzyme.

It can be useful particularly where exocrine pancreatic insufficiency is suspected.

But the result can be misleadingly low in a very watery stool, so the test has to be assessed together with the clinical findings.

How is it treated?

Treatment of steatorrhoea is directed at its cause.

If pancreatic enzyme insufficiency is found, pancreatic enzyme preparations can be used in suitable patients. Entirely different treatments may be needed in other conditions — a gluten-free diet in coeliac disease, relief of the obstruction in bile duct obstruction.

It is therefore not right for someone to start pancreatic enzyme or any other treatment themselves on the basis that their stool looks greasy.

When should a doctor be seen?

Fatty stools are worth assessing if they do not settle within a few days or if they keep coming back.

The underlying cause should be investigated particularly where there is unintentional weight loss, marked abdominal pain, persistent diarrhoea, jaundice, anaemia, fatigue or malnutrition alongside it.

Remember: fatty stools are not a diagnosis. The causes range from pancreatic enzyme deficiency to diseases of the small intestine and disturbances of bile flow. The cause of the steatorrhoea has to be established first for the treatment to be right.