Dietary fat and cecal microbial activity in the rat

Weanling rats were fed low-fat (1% w/w safflower oil) or high-fat (1% w/w safflower oil plus 35% w/w beef fat or cocoa butter) diets for 30 days, and the activities of five cecal microbial enzymes were determined. When compared with the low-fat diet, beef fat significantly increased total cecal beta-glucuronidase activity, but cocoa butter, with a similar fatty acid composition, did not. Both high-fat diets significantly decreased total cecal azoreductase, beta-glucosidase, and nitrate reductase activities, but neither significantly affected urease activity. When expressed as specific activities (per 10(11) bacteria), cocoa butter decreased azoreductase, and beef fat caused increases of beta-glucuronidase and urease. Beef fat, but not cocoa butter, significantly reduced cecal bacterial numbers when compared to the low-fat diet. Both high-fat diets led to equivalent reductions in the proportion of aerobic bacteria.