Weickert MO et al. (2005) Impact of cereal fibre on glucose-regulating factors. Diabetologia 48: 2343–2353

Insulin secretion after eating is stimulated by increased blood glucose and secretion of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1). Insoluble fiber is associated with a reduced risk of type 2 diabetes, but interpretation of the effects of whole grains on glucose metabolism can be difficult, because of the presence of other potentially active ingredients, such as protein, antioxidants and phytoestrogens.

Researchers in Germany have studied the effect of purified insoluble cereal fibers on glucose, insulin, GIP and GLP-1 in 14 healthy women with normal glucose tolerance. On six to eight occasions, subjects consumed three matched portions of bread enriched with wheat fiber, oat fiber, resistant starch, or control bread, and the next day consumed three portions of control bread. The insulin response on day 1 was earlier for both wheat and oats than for control. GIP response was also earlier after oat-fiber consumption, but GLP-1 was not affected by any fiber. Those who consumed fiber-enriched bread on day 1 had a reduced glucose response after consumption of control bread on day 2. Fiber enrichment had no effect on insulin, GIP or GLP-1 levels on day 2.

The authors suggest that improved glucose handling might result from increased insulin sensitivity or non-insulin-dependent glucose uptake. They conclude that diet enrichment with insoluble cereal fiber offers a means to improve carbohydrate metabolism, but that the findings need to be confirmed in larger studies that include diabetic patients. More work is also needed to discover the mechanisms underlying the effects seen in the study.