Cholesterolemic effects of the lysine/arginine ratio in rabbits after initial early growth

The lysine/arginine ratio has been directly associated with serum cholesterol levels. Male, New Zealand rabbits with a mean weight of 2.1 kg were fed, ad libitum, one of three diets containing 14% vegetable oil and 20% protein from casein, soy or almonds with lysine/arginine ratios of 2.2, 0.9, or 0.3, respectively. At the end of three weeks for phase 1, the serum cholesterol level of the casein group (154 +/- 25 mg/dl, mean +/- SD) was twice the level and significantly greater (p less than 0.02) than either of the plant protein groups (soy 70 +/- 7, almond 78 +/- 6 mg/dl). During phase 2, the almond diet was supplemented with L-lysine to increase the lysine/arginine ratio from 0.3 to 3.0 while casein remained as the high, and soy the low lysine/arginine ratio control diets. Serum cholesterol levels remained high for the casein, and low for the soy groups, while lysine supplementation significantly increased (p less than 0.05) the serum cholesterol level in the almond protein group (from 78 +/- 6 to 101 +/- 10), but not greater than the casein group. Growth was similar for rabbits fed soy or casein diets throughout the study, but lower (p less than 0.02) for the almond group. Thus, growth rate was not related to the effect of dietary protein on levels of serum cholesterol. While there is a direct relationship between hypercholesterolemia and the absolute amount of dietary lysine and with the lysine/arginine ratio, the data suggest that this is only a partial explanation for the effect of proteins on the control of serum cholesterol levels.