The effect of dietary protein source and saponins on serum lipids and the excretion of bile acids and neutral sterols in rabbits.

1. Four groups of six rabbits were given purified diets in which the dietary variables were protein source (isolated soya-bean protein or cow's-milk protein) with or without saponin supplementation (10 g/kg). 2. Rabbits given soya-based diets showed significantly lower serum concentrations of triglyceride and cholesterol (P less than 0.01). The latter changes were confined to the cholesterol fractions of beta-lipoproteins. 3. These changes in serum cholesterol were associated with a significantly increased excretion of acid and neutral sterols in animals given soya-bean protein. 4. There was no evidence to suggest that the effect of dietary protein source on serum lipids and the excretion of total and individual sterols was influenced by saponin supplementation. 5. These results do not support the hypothesis that the hypocholesterolaemia associated with plant proteins is due to the presence of saponins.