Fructose Malabsorption - Pathophysiology

Pathophysiology

Fructose is absorbed in the small intestine without help of digestive enzymes. Even in healthy persons, however, only about 25-50g of fructose per sitting can be properly absorbed. People with fructose malabsorption absorb less than 25g per sitting. In the large intestine, fructose that has not been adequately absorbed reduces the absorption of water osmotically and is metabolized by colonic bacteria into short chain fatty acids, producing the byproduct gases hydrogen, carbon dioxide and methane. This abnormal increase in hydrogen is detectable with the hydrogen breath test.

The physiological consequences of fructose malabsorption include increased osmotic load, rapid bacterial fermentation, altered gastrointestinal motility, the formation of mucosal biofilm and altered profile of bacteria. These effects are additive with other short-chain poorly absorbed carbohydrates such as sorbitol. The clinical significance of these events depends upon the response of the bowel to such changes; they have a higher chance of inducing symptoms in people with functional gut disorders than asymptomatic subjects. Some effects of fructose malabsorption are decreased tryptophan, folic acid and zinc in the blood.

Restricting dietary intake of free fructose and/or fructans may provide symptom relief in a high proportion of patients with functional gut disorders.