The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 9 No.
4 • December 2006
Indigestible Carbohydrates Contribute to Improved Glycemic Response at Next Meal
A meal’s ability to diminish the glucose response to carbohydrates eaten during the following meal is known as the “second-meal effect.” Low-glycemic-index foods reduce blood glucose in response to a first meal, and this has been suggested to be the mechanism for a second-meal effect. However, as the authors of a recent paper on indigestible carbohydrates point out, low-glycemic-index foods often increase colonic fermentation because of the presence of fiber and resistant starch. (For example, our Glycemic Control barley products are very low-glycemic—with about the same glycemic index as lentils—and increase colonic fermentation.) The authors designed a study using ten healthy volunteers to study the effect of fermentation on the second-meal effect independently of its effects on glycemic index.
The volunteers ate three different breakfast meals consisting of sponge cakes made with rapidly digestible, nonfermentable amylopectin starch plus cellulose (the high-glycemic-index meal) or rapidly digestible, nonfermentable amylopectin starch plus the fermentable disaccharide lactulose (high-glycemic-index + Lac), or slowly digestible, partly fermentable amylose starch plus cellulose (the low-glycemic-index meal). Five hours later, the subjects were given a standard lunch containing 93 grams of digestible carbohydrates.
The results showed that both the high-glycemic-index + Lac meal and the low-glycemic-index meal improved glucose tolerance at lunch. In the case of the high-glycemic-index + Lac meal, the effect was associated with low nonesterified fatty acids and delayed gastric emptying. The authors concluded that “Fermentable carbohydrates, independent of their effect on a food’s glycemic index, have the potential to regulate postprandial responses to a second meal by reducing nonesterified fatty acid competition for glucose disposal and, to a minor extent, by affecting intestinal motility.” [Note: A big difference between the low-glycemic-index meal used here and our Glycemic Control barley is that the fiber added to the resistant (amylose) starch was nonfermentable purified cellulose, which is an insoluble rather than soluble fiber such as beta-glucan; beta-glucan increases viscosity, unlike cellulose, and also has immune-stimulating effects that cellulose does not have.]
In their discussion, the authors mention an earlier study by Robertson et al. in which amylose-resistant starch enhances carbohydrate processing even 12 hours in the postprandial period, which suggests that the effect could be due to colonic fermentation. It has been reported that low-glycemic-index meals containing nondigestible fiber eaten at night can improve the glucose response to a morning meal.
- Brighenti et al. Colonic fermentation of indigestible carbohydrates contributes to the second-meal effect. Am J Clin Nutr 83:817-22 (2006).
- 2. Robertson et al. Prior short-term consumption of resistant starch enhances postprandial insulin sensitivity in healthy subjects. Diabetologia 46:659-65 (2003).
- Nilsson et al. Effects of GI and content of indigestible carbohydrates of cereal-based evening meals on glucose tolerance at a subsequent standardised breakfast. Eur J Clin Nutr 60(9):1092-9 (2006).