We have evaluated the influence of oligofructose (OFS), a fermentable dietary fibre, on glucose homeostasis, insulin production and intestinal glucagon-like peptide-1 (GLP-1) in streptozotocin-treated diabetic rats. Male Wistar rats received either i.v. streptozotocin (STZ; 40 mg/kg) or vehicle (CT); one week later, they were fed for 6 weeks with either the standard diet (STZ-CT), or with a diet containing 10% oligofructose (STZ-OFS); both diets were available ad libitum. In a second set of experiments (duration 4 weeks), a supplemental group of food-restricted rats (STZ-Res) receiving a similar intake as CT rats, was added. OFS improved glucose tolerance and reduced food intake as compared with STZ-CT rats in both the post-prandial state and after an oral glucose tolerance test. After 6 weeks, portal and pancreatic insulin concentrations were doubled in STZ-OFS rats. Food restriction improved these parameters when compared with STZ-CT rats, but to a lesser extent than in the STZ-OFS group. We have shown that OFS treatment increased portal and colonic GLP-1(7-36) amide levels and doubled colonic proglucagon and prohormone convertase 1 mRNA levels; both OFS and food restriction lowered ileal GLP-1(7-36) amide levels as compared with levels in STZ-CT rats. We propose that OFS, through its fermentation in the colon, promotes the expression and secretion of colonic peptides, namely GLP-1(7-36) amide, with beneficial consequences on glycaemia, insulin secretion and hyperphagia in diabetic rats.