Inhibition of starch digestion by alpha-amylase inhibitor reduces the efficiency of utilization of dietary proteins and lipids and retards the growth of rats.

Digestion/absorption and nutritional utilization of starch, protein and lipids were studied in rats fed diets containing purified kidney bean alpha-amylase inhibitor at levels of 0, 1.6, 3.3 and 6.6 g/kg diet. At the two higher levels, the growth rate of rats and the apparent digestibilities and utilization of dietary starch and protein were significantly less than in control rats, and losses of nitrogen, lipids and carbohydrate resulted in a significant reduction in dry body weight. Some organs of the body were also affected: the relative dry weights of the intestines and the pancreas were higher, whereas liver and thymus weights were lower than in control rats. As starch digestion in the small intestine was negligible at higher inhibitor concentrations, the cecum was practically blocked by solidified digesta. This effect and the ensuing bacterial fermentation stimulated the growth of this tissue by hyperplasia and hypertrophy. However, as the distension was not always sufficient, the organ was occasionally ruptured and the rats had to be killed. Inhibitor doses in this work were comparable to those in clinical studies, implying that the use of the inhibitor is not without health risks. Moreover, diets rich in alpha-amylase inhibitor such as those containing transgenic plants with high levels of inhibitor gene expression cannot be recommended in intensive animal production.