A number of traditional diets have been studied regarding beneficial effects on postprandial glycaemia, including those of the Mediterranean, Pacific Island (Okinawan) and Australian bush regions. Evidence suggests that traditional diets are beneficial to the health because they contain few refined carbohydrates and little sugar. The non-digestible to digestible carbohydrate ratio, or fibre to starch ratio, is high in traditional diets, whereas in the Western diet this ratio is low. This may be the reason that lifestyle diseases are common in developed nations but almost completely absent from populations that still consume their traditional diets. In nature, where sugar is present it is nearly always accompanied by high amounts of fibre, as demonstrated by fruits and some vegetables. Honey is the only real source of non-fibre containing sugar in nature, and this is rare and protected by bees.
For example, researchers1 investigated the digestive rates of the starch in 20 Australian aborigine foods, 10 pacific island foods and 7 Western foods. Using an in vitro digestibility model allowed the study authors to compare relative digestion times. Of the 30 traditional foods, 23 were digested more slowly than the 7 Western foods. These results support the contention that the benefits of traditional diets may be due to the slower rates of starch digestion. Comparison of 8 bush foods with potatoes showed that 6 of the bush foods produced lower 3 hour postprandial glucose curves in healthy subjects. A reduction in the glycaemic effects of foods may decrease insulin release, and this may in turn prevent the development of insulin resistance. Slow digesting starch may therefore be protective of metabolic syndrome, obesity and diabetes.
The benefits of lower postprandial glycaemia is illustrated by studies investigating the health effects of legumes. In the above study some of the more slowly digested starch containing foods were members of the legume family. Research shows that legumes have comparatively slow digestion rates and produce low blood glucose and insulin responses compared to non-legume starches. Legumes have a high fibre to starch ratio, and this may account for some of their beneficial glycaemic effects. However, they also have other properties that may contribute to reduced glycaemia. For example, legumes have a high content of protein, and this may increase the release cholecystokinin from I cells of the small intestine. Cholecystokinin may then inhibit gastric emptying though negative feedback, thus delaying food transit. In addition, some legumes contain digestive enzyme inhibitors, and this may decrease the absorption of starch and sugars from the gut.
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