The glycaemic index: importance of dietary fibre and other food properties

An increasing body of evidence suggests that a low-glycaemic-index (GI) diet has a therapeutic as well as a preventive potential in relation to the insulin resistance syndrome. The implementation of a low-GI diet, however, will require an extended list of low-GI foods to be available on the market. The tailoring of low-GI bread products offers a particular challenge due to their generally high GI and abundance in the diet. Low-GI bread products can be tailored by, for example, enclosure of cereal kernels, sourdough fermentation and/or addition of organic acids, or use of cereal genotypes with elevated contents of amylose or β-glucans. Low-GI cereal foods appear to vary in effect on ‘second-meal’ glucose tolerance in healthy subjects. In addition to the slow release properties of such foods, the content of dietary fibre appears to play a role. The low glycaemia to starch in a pasta breakfast (GI 54) promoted a higher glucose tolerance and lowered triacylglycerol levels at a standardized lunch ingested 4 h later, compared with a white-wheat bread breakfast (GI 100). The metabolic benefits of the low GI properties per se have been demonstrated also in the longer term. Thus, a reduction in dietary GI improved glucose and lipid metabolism and normalized fibrinolytic activity in type 2 diabetics, while maintaining a similar amount and composition of dietary fibre. However, the higher dietary fibre content frequently associated with low-GI foods may add to the metabolic merits of a low-GI diet. Consequently, a low-GI barley meal rich in dietary fibre (GI 53) improved glucose tolerance from evening meal to breakfast, whereas an evening meal with pasta had no effect (GI 54). The exchange of common high-GI bread for low-GI high-fibre bread, as the only dietary modification, improved insulin economy in women at risk of type 2 diabetes. These results are in accordance with epidemiological evidence of a reduced risk of type 2 diabetes with a low-GI diet rich in cereal fibre. It is concluded that low-GI cereal foods developed should preferably be rich in dietary fibre.