1. Dietary fibre has a moderating impact on glucose metabolism. To test the hypothesis that this effect of fibre may be mediated by its breakdown product acetate, oral glucose tolerance tests were carried out in healthy volunteers with and without acetate.
2. Five subjects received 50 g of glucose orally while taking either acetate (15 mmol every 15 min) by mouth or chloride as control. Oral acetate made no detectable difference to glucose tolerance or to levels of free fatty acids, 3-hydroxybutyrate, lactate, insulin, glucagon and gastric inhibitory polypeptide.
3. The 50 g dose of glucose temporarily depressed acetate levels in blood. This was probably due to an interaction between glucose and acetate in the gastrointestinal lumen as the same effect was seen with 50 g of xylose in three subjects.
4. Plasma acetate concentrations were unaffected by 50 g of oral glucose in one subject when acetate was instilled into the sigmoid colon.
5. It is unlikely that the improvement of glucose tolerance by dietary fibre is mediated by acetate.