What is insoluble insulin

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Abstract of the lecture by Prof. Dr. med. Andreas F. H. Pfeiffer at a symposium of Abbott Diabetes Care at the 42nd annual conference of the German Diabetes Society (DDG) in Hamburg.

Insoluble fiber could play a significant role in the future

In large epidemiological studies, dietary fiber shows a close connection with the risk of diabetes mellitus as well as atherosclerosis. Notably, grain fiber appears to explain most of these effects. On the other hand, fiber from fruits and vegetables probably plays a smaller role. Dietary fiber can be divided into soluble and insoluble fiber, depending on its physicochemical properties. In the past, soluble fiber was mostly associated with an improvement in lipid profile, a reduction in LDL cholesterol, and an improvement in triglycerides. Insoluble dietary fiber, which consists predominantly of cellulose and hemicellulose, was largely considered to be inactive, without this having been examined in more detail.

Soluble fiber changes the viscosity of the food pulp and can thereby affect the rate at which food is absorbed. According to some studies, dietary fiber delays the glycemic index by changing the way glucose is absorbed. A typical such fiber is e.g. B. arabinoxylan, obtained from wheat or oats. In prospective interventional studies with a cross-over design, in which 15 g of arabinoxylan were additionally given per day, we observed an improvement in the effectiveness of insulin and a more favorable course of the fat profile throughout the day. Furthermore, the arabinoxylan interfered with the ghrelin levels, a satiety hormone from the stomach. In contrast, there were no changes in adiponectin or cytokines or in CRPs.

Insoluble fiber could play a more significant role in the future after we observed an astonishingly pronounced effect on insulin sensitivity in studies. Subjects received 30 g of insoluble fiber baked in bread in a blind prospective design. The insoluble fiber had no acute effect on the glycemic index, but changed insulin secretion somewhat in the sense that the insulin peak appeared faster and earlier. This change in insulin secretion was caused by a changed secretion pattern of the gastric inhibitory polypeptide. On the second day, the subjects received a standardized test of the glycemic index with 50 g of carbohydrates in the form of white bread, and this now showed a significant improvement in insulin sensitivity. This was not based on a change in glucose uptake, as was described for soluble fiber, but on an acceleration of the glucose disappearance rate, i.e. an improvement in the effectiveness of insulin. Since these data were calculated from meal tests, we repeated the studies with obese patients who received insoluble fiber for three days and then a hyperinsulinemic euglycemic clamp. This confirmed the significant improvement in insulin sensitivity without any significant change in other biomarkers of the metabolic syndrome such as adiponectin or cytokine. However, there were significant changes in various satiety hormones.

Comparable studies on diabetics were carried out with a less complex design, but also showed a clear improvement in glucose metabolism. Fiber is a simple class of substances with an astonishingly strong positive effect on metabolism and, in epidemiological studies, also on endpoints such as diabetes and cardiovascular risk. Increasing the intake of dietary fiber is therefore a very feasible and interesting concept for improving the quality of food in both metabolic syndrome and manifest diabetes mellitus.

Caption: Prof. Dr. med. Andreas F. H. Pfeiffer, Charité - Universitätsmedizin Berlin, Department of Endocrinology, Diabetes and Nutritional Medicine.
Image source: Abbott Diabetes Care

last edited: May 16, 2007