EFFECT OF ADDITION OF BREWERS-YEAST TO SOY PROTEIN AND CASEIN ON PLASMA-CHOLESTEROL LEVELS OF RABBITS

The purpose of this study was to determine whether the addition of hig h levels of yeast to casein and soy diets could modify the well known effects of any of these proteins on plasma cholesterol. Rabbits, were fed either a diet containing soybean protein-brewer's yeast or casein- brewer's yeast (each protein source providing 50 percent of the dietar y nitrogen content) and casein and soybean protein basal diets. Brewer 's yeast was obtained from a local beer factory in its non-debittered form. The diets contained 20 percent protein, 9 percent coconut oil an d 1 percent com oil, with no added cholesterol. After a 22 day experim ental period, rabbits fed casein developed hypercholesterolemia wherea s those fed the soybean protein diet did not. The replacement of 50 pe rcent of the soy nitrogen by brewer's yeast nitrogen, increased the to tal cholesterol plasma level, but significant differences were only ob served between rabbits fed casein and casein-yeast and those fed soybe an protein. No differences in high density lipoprotein cholesterol cou ld be detected among the groups. However, the HDL-cholesterol/total ch olesterol ratio was significantly reduced in response to soy substitut ion by brewer's yeast. The (low density lipoprotein + very low density lipoprotein) - cholesterol was increased in all groups whith the exce ption of the animals fed purely soy protein. These data suggest a hype rcholesterolemic activity of the dietary non-debittered brewer's yeast . Nevertheless, according to the amino acid composition, the factor re sponsible for the reported effects of dietary yeast was not associated with a high lysine to arginine ratio which could be due to extracellu lar components.