Fructose intolerance happens when the fruit sugar fructose is poorly absorbed in the small intestine causing symptoms of diarrhoea, bloating and wind. Fructose is not fully absorbed in most people, but does not usually give rise to symptoms.  In children and some sensitive people, too much fructose and sucrose from high intakes of certain fruits produces these unpleasant symptoms.

Malabsorption of sugars

Malabsorption describes the difficulty in enzymatic digestion (breaking food down) and subsequent absorption (into he blood stream via the liver) of nutrients from food. Fructose Intolerance refers to the limited absorption of fructose, either due to limits in the transport system or too much fructose in the diet. Fructose is a simple sugar, which does not need enzymatic digestion before is can be absorbed.  Sucrose, commonly know as sugar, is a two sugar units and needs enzymatic digesting before it can be absorbed.  Sucrose is made of one fructose unit and one glucose unit and so consuming excess sugar itself may give rise to similar symptoms.

What are the symptoms and dietary treatment?

Fructose that passes into the large intestine unabsorbed in the small intestine, provides food for the intestinal bacteria, which ferment the sugar into gases and acids.  This causes a number of unpleasant symptoms including bloating and wind caused by the production of gas; abdominal pain due to bloating but also urgent, explosive, watery stools. The treatment is a diet low in fructose, achieved by reducing fruit and vegetable intakes, especially fruit juices, dried fruit and honey. It is not recommended or easy to exclude fructose from the diet completely, because fruits and vegetables are part of a healthy diet. Following a diet low in fructose for several weeks, once symptoms have completely resolved, fructose may be reintroduced in a controlled way.