Lowering of Serum Cholesterol and Triglyceride Levels by Balancing Amino Acid Intake in the White Rat

Earlier studies in rats have shown that serum cholesterol levels were significantly lower in rats fed an L-lysine-supplemented ration. This investigation was initiated to determine if the reverse was true. We reasoned that the addition of an incomplete protein to a complete rat ration would bring about an increase in serum lipid levels. This would result from the intermediary metabolic conversion of systemic amino acids not used in protein synthesis. We further postulated that supplementation of the imbalanced protein would obviate the hyperlipidemia. Gelatin was chosen as the incomplete protein since it is deficient in tryptophan, an essential amino acid. Adult male Sprague-Dawley rats fed rations with added gelatin (5, 15 and 25%) for 30 days showed significant increases in serum cholesterol and triglyceride levels. Lipid levels in rats fed L-tryptophan-supplemented diets containing the same levels of gelatin did not differ from those animals fed the control ration. The data indicate that hyperlipidemia results from the feeding of imbalanced protein. Such hyperlipidemia can be obviated by supplementation with the limiting amino acid.