Editor,—We read with interest the paper by Gweeet al (Gut1999;44:400–406) which described the role of psychological and biological factors in postinfective irritable bowel syndrome (IBS). However, these authors did not study fructose or lactose malabsorption in relation to duodenal function. Carbohydrate malabsorption syndromes—for example, fructose and/or lactose malabsorption, are frequently linked to IBS.1 Patients with fructose malabsorption often have a clear history of postinfective onset of their symptoms, as Gwee and colleagues found in patients with IBS.

We have shown an association between carbohydrate malabsorption syndromes and early signs of mental depression2 3; similarly, Gwee et al found significant links between anxiety, depression, and somatisation scores in patients with IBS. Our data suggest that non-absorbed carbohydrates interfere with tryptophan metabolism, which may explain the development of …