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Stool concern: Diet affected?

I have read that loose, pale-coloured stools are a sign of fat malabsorption. I have had consistently yellow, foul-smelling stools (with undigested bits in them) for as long as I can remember. Also, after going to the toilet I often feel nauseous. What could be the cause? Does it mean that my body is deficient in "good fats" and vitamins?

Dr Fred Kavalier answers your health question:

When the intestine is unable to properly digest and absorb fats, the stools become pale, bulky and smelly. They usually float in the lavatory pan, and are difficult to flush away. Sometimes it is even possible to see floating oil droplets in the toilet water. Fat malabsorption can be caused by many different problems. If the pancreas or liver are not working properly, in conditions such as cystic fibrosis and liver disease, the intestine is unable to break down and absorb food. In conditions such as coeliac disease, which is caused by an abnormal reaction to wheat and other foods that contain gluten, the intestine loses its ability to absorb nutrients. If people with coeliac disease avoid all foods containing gluten, the intestine recovers and regains its ability to absorb food normally. Some vitamins, especially A, D and K, are fat-soluble vitamins: if you are not absorbing fat properly, you can become deficient in these vitamins. You need to have tests to see if you are suffering from malabsorption. If you are, then the cause needs to be identified and treated. Your first stop should be your GP. The next stop should be a gastroenterologist.

Please mail your questions for Dr Fred to health@independent.co.uk. He regrets that he is unable to respond personally to questions.