Lipid Accumulation in the Liver of Rats Fed a Soy Protein Isolate Diet with Excess Cystine, and its Prevention by Methionine or Choline.

The effects on liver and serum lipids of rats of excess cystine added to their casein or soy protein isolate diets were studied. When excess cystine was added to the casein diet, liver lipids were not changed. Using soy protein isolate as a protein source, both food consumption and body weight gain were depressed with increasing levels of dietary cystine. Liver total lipids, cholesterol, triacylglycerols, and phospholipids were increased in rats with 2.5% or 3.5% cystine diets. Serum cholesterol of rats on the 3.5% cystine diet was significantly higher than those of the other groups, which yielded similar values. Serum triacylglycerols were increased by the addition of 0.5% or 1.5% cystine, and decreased by the addition of 2.5% or 3.5% cystine to the diet. Serum free fatty acids increased or tended to increase when liver lipid accumulation was observed. The addition of either methionine or choline to the cystine-excess diet containing soy protein isolate prevented the accumulation of triacylglycerols and phospholipids in the liver although serum triacylglycerols did not return to the levels of rats on the diet without cystine, and serum free fatty acid levels were not changed. Thus, it is surmised that this fatty liver might be due to the choline deficiency induced by the excess cystine.