ll carbohydrate foods provide 3.75 calories per gram. Proponents of the forced energy restriction diet hypothesis will argue that a calorie is a calorie and it is the balance of energy consumed and energy expended that will dictate weight gain. However, evidence in the scientific literature does not support this viewpoint, but instead suggests that it is the quality of the food that is eaten that is the primary determinant of weight gain. Different carbohydrate foods can have quite different effects on body composition because they are able to affect blood sugar levels in very different ways, and this may have subsequent implications for weight gain. Carbohydrate foods that cause a more controlled glycaemic response tend to be higher in fibre, and higher intakes of such foods are associated with a lower body weight. Beans have been shown repeatedly to produce a lower glycaemic response compared to other foods.
For example, one group of researchers1 compared the glycaemic effects of beans and potatoes on 6 healthy male subjects. Kidney beans were made into mash to hide their origin and the subjects consumed these or commercially available potato flakes. A significantly lower blood glucose response was seen after consumption of the beans, when compared to the potato flakes, and this resulted in a smaller area under the curve for the beans. This was reflected in a lower plasma insulin response following the beans, although the total area under the curve for insulin in both groups was not significantly different. To test whether the lower glycaemic response to the beans was due to delayed gastric emptying, the researchers mixed 51Cr with the meal and monitored its progress using a gamma camera. However, there was no difference between the emptying rate of beans or potato flakes.
These results support other data in showing a glycaemic benefit to eating beans. Because the gastric emptying rate of beans was similar to potato flakes, this suggests that this is not the reason for the lower blood sugar response. Therefore, the digestion and absorption of the beans is likely handled more slowly in the small intestine, when compared to other carbohydrate foods. In this study the beans contained 13.5 and 5.8 grams of insoluble and soluble fibre, respectively. The potato meal contained only 2.8 grams of insoluble fibre and 1.8 grams of soluble fibre. However, when meals containing equal amounts of fibre are compared, beans still produce lower glycaemic responses, suggesting that fibre is not the cause for the difference. Beans contain the carbohydrate L-arabinose that is able to inhibit the enzyme sucrase, and also possess amylase inhibitors, and these may slow the digestion and absorption of carbohydrates.
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