Abstract
The effect of dietary methionine on cholesterol and free amino acid levels in blood plasma was studied in Donryu rat fed 10% and 25% casein and soy protein isolate diets with or without cholesterol.
In the tests carried out in the absence of cholesterol, the supplementation of methionine gave no change to the plasma cholesterol level of the rats fed on 10% and 25% of casein diets and 25% soy protein isolate diet, while a significant decrease in the cholesterol level in plasma of rats fed on a 10% soy protein diet with methionine was observed.
On the other hand, the cholesterol level in plasma was significantly raised by the supplementation of cholesterol to any of the above-mentioned diets, especially when the rats were fed on 10% protein level. In this case, an increased cholesterol level in plasma due to the addition of cholesterol to diets was significantly prevented by the supplementation of methionine.
Decreases of threonine and serine, and an increase of taurine in plasma free amino acids were observed by the supplementation of methionine to 10% casein diet and also to 10% soy protein isolate diet regardless of the supplementation of cholesterol. The same phenomenon was found in the rats fed on the 25% cholesterol free soy protein isolate diet with no supplementation of methionine.
The addition of cholesterol to diet caused a specific decrease in the plasma threonine level, which seems to be independent of protein levels in diet.
