Digestion rate of legume carbohydrates and glycemic index of legume-based meals.

A study was performed to examine the rate of digestion of available carbohydrate in legumes and its mixtures with cereals, prepared as commonly eaten. The legumes and cereals studied were lentil (Lens sculenta), pea (Pisum sativum), bean (Phaseolus vulgaris, var tortola), rice (Oryza sativa) and spaghetti. Foods were purchased at the city market. Total starch content and the carbohydrate digestion rates were determined using the enzymatic method proposed by Englyst et al. Total starch levels ranged from 7.78 g/100 g in cooked flour bean to 20.6 g/100 g in a bean-spaghetti dish, and dietary fiber contents ranged from 2.4 g/100 g in a cooked 70:30 lentil-rice mixture to 5.26 g/100 g in a cooked whole bean. The rapid digestion rate carbohydrates showed values from 4.8 in the bean soup to 8.9 in the bean-spaghetti combination. The same results show, expressed as rapid available glucose (RAG), the amount of rapid carbohydrate/100 g food or meal as eaten, and as the starch digestion index (SDI), the percentage of rapid carbohydrate digestion rate in relation to the total amount of carbohydrate. The RAG values ranged between 5.0 for cooked beans and 10 for cooked beans and spaghetti, and the SDI ranged between 40 for cooked pea flour and 62 for cooked bean flour. Legumes prepared as soup showed a higher rapid digestion rate than legumes prepared as whole grain. The bean-spaghetti based-meal and the lentil-based meal showed glycemic index mean and standard deviation values of 76.8 +/- 43.4 and 49.3 +/- 29.5, RAG values of 7.0 and 6.0, and SDI values of 57 and 54, respectively. The knowledge of the importance of the carbohydrate digestion rates in human health in increasing, and probably will soon be used in the development of the food pyramid. The foods with a moderate fraction of rapid digestion rate, such as legumes, should be included in the base of the pyramid.