Effects of Dietary Amino Acid Composition on Antiamaranth Activity of Beet Fiber in Rats

The effect of the source of dietary protein on the antitoxic activity of beet fiber was examined in rats given purified feed containing 5% amaranth (Food Red No.2) for 5 weeks. Three basal diets were used : 25% casein, soybean protein isolate (SPI), and 25% wheat gluten. The addition of 5% amaranth to these basal diets caused growth retardation, which was greatest in rats fed SPI plus amaranth. The addition of 5% or 10% beet fiber to the diet with SPI plus amaranth overcame growth retardation slightly. The addition of 0.22% L-methionine to the diet with SPI plus amaranth overcame such retardation almost completely. The further addition of 5% beet fiber to this diet with supplementary methionine completely restored growth. The addition of 0.22% methionine to the diet with casein plus amaranth did not improve growth. The addition of 5% beet fiber to the diet with casein plus amaranth allowed growth comparable with that of control rats on the basal diet of casein. Dietary amaranth accelerated small intestinal transit speed, found by measurement of the distance that the meal front had traveled through the lumen of small intestine from the pylorus 10 min after intubation. The addition of beet fiber to feed containing amaranth, however, prevented this acceleration. These results suggest that the anti-amaranth activity of beet fiber is affected by the amino acid composition of the dietary protein source.