Neutral sterol excretions in rats fed skim milk and skim milk yogurt diets.

Acceleration of cholesterol catabolism (through feces) has been proposed as one of the mechanisms for the hypocholesterolemic effect of dairy products. This study examined the effects of feeding two milk products (skim milk and skim milk yogurt) on fecal neutral sterol excretions in rats. Six groups of nine rats each were fed iso-caloric Chow-based diets containing water, 45% skim milk (SM), or 45% skim milk yogurt (SMY), without or with cholesterol. The results indicate that both SM and SMY increased the excretion of total neutral sterols under hyperlipemic conditions. The SMY diet (with cholesterol) also increased the excretion of coprostanol, a bacterial metabolite.

Effects of skim milk, skim milk yogurt, orotic acid, and uric acid on lipid metabolism in rats.

The effects of feeding two milk products (skim milk and skim milk yogurt) and two proposed hypocholesterolemic factors (orotic acid and uric acid) on serum cholesterol (HDL, LDL, total, HDL/Total and HDL/LDL), liver lipids (total liver lipids and liver cholesterol), and aortal cholesterol were studied. Ten groups, of nine rats each, were fed isocaloric Chow-based diets containing water, 45% skim milk (SM), 45% skim milk yogurt (SMY), and 0.0025% orotic acid (OA) or 0.001% uric acid (UA), without or with cholesterol. The SM diet (with cholesterol) resulted not only in lower total cholesterol (P < 0.10), LDL cholesterol (P < 0.05), aortal cholesterol (P < 0.01), and liver cholesterol (P < 0.10), but also in increased HDL (P < 0.05) and HDL/LDL (P < 0.10) cholesterol ratio. The SMY diet, on the other hand, resulted in lowered total serum cholesterol (P < 0.05) and aortal cholesterol (P < 0.01) and in higher LDL (P < 0.05) cholesterol. The hypocholesterolemic effects were more marked for SM than for SMY. Addition of OA and UA to diets increased serum cholesterol, LDL cholesterol, and total liver lipids; the OA diet also increased liver cholesterol. Neither OA nor UA alone was the factor responsible for the hypocholesterolemic effects seen with SM and SMY feeding.

Effects of dietary fiber, carbohydrate, lipid and protein levels on serum and liver lipids in rats.

Response-surface regression analysis was used to study dietary levels of fiber, carbohydrate, lipid and protein to minimize serum and liver cholesterol and triglyceride levels and maximize serum high-density lipoprotein-cholesterol levels of male weanling rats. Because the dietary components were not statistically independent, they were studied in combinations of three variables. The three-variable combinations were the most useful in locating the desired maximum or minimum lipid responses in terms of the proportions of the dietary components. These analyses indicated that dietary carbohydrate, lipid and protein were better than dietary fiber for predicting the serum and liver lipid response levels. Response-surface contours and three-dimensional plots were developed for each lipid response except serum triglycerides, which were not predictable. The contours and three-dimensional plots were used to help determine those combinations of the diet components that would produce the desired maximum or minimum lipid responses. The statistical analyses indicated that the desired lipid response levels could be attained with a diet consisting of 3-5% neutral detergent bran fiber, 6-10% lipid, 54-55% carbohydrate, 26-30% protein and 4.7% vitamins and minerals.