Effect of dietary fat saturation on absorption and intestinal secretion of cholesterol by the hypercholesterolemic rat

Relationship between changes in plasma lipoprotein concentrations and fecal steroid excretion in man during consumption of four experimental diets

Limited information is available on the mechanism by which changes in nutrient intake influence plasma lipids. We compared the effects on plasma lipoprotein levels of 3 dietary modifications involving changes in total fat intake (27-40% of calories), cholesterol intake (100-250 mg/1000 kcal), the dietary polyunsaturated to saturated fatty acid ratio (0.3-1.0) and intake of vegetable-derived fiber and protein. On these 3 diets, plasma low density lipoprotein was reduced by 26-34%. Fecal bile acid excretion was similar on all diets (363-379 mg/day). There was no alteration in fecal bile acid output associated with an increase in polyunsaturated or total fat intake. Sterol balance became significantly more negative during consumption of only 1 of the 3 cholesterol-lowering diets. The observed reduction in plasma cholesterol levels was not associated with an increase in fecal bile acid output suggesting that diet-induced changes in circulating cholesterol are not maintained by an increase in sterol turnover but may reflect alterations in hepatic cholesterol and lipoprotein synthesis.

Effects of dietary fat on amounts of cholesterol transported by mesenteric lymph in calves fed milk

Five nonruminating male calves were prepared surgically with shunts from mesenteric lymph duct to posterior vena cava and sequentially were fed diets of reconstituted skim milk and skim milk plus supplemental cholesterol plus soybean oil, beef tallow, or milk fat. Calves received skim milk for 2 days, followed by the other diets for 4 days each in a predetermined order. On the 2nd and 4th day each diet was fed, lymph was collected hourly for 8 h, starting 1 h before the morning feeding. Cholesterol transported in lymph increased markedly in the hour after feeding and then declined rapidly but to quantities still greater than pre-feeding. Average cholesterol in lymph was 1.7, 2.8, 3.7, and 4.2 mg/(h X kg body weight) for the skim milk, soybean oil, tallow, and milk fat diets. No difference was significant between 2nd and 4th day totals for each diet. Because cholesterol rate of flow quickly responded to new diets and stabilized within 2 days, this technique permitted evaluation of effects of dissimilar dietary fats upon amounts of cholesterol and triglyceride transported by mesenteric lymph.

[Effect of high-fat diet on the contents of total cholesterol, free cholesterol and esterified cholesterol in the serum and liver of rats]

Four-week-old male Wister Rats were fed a diet containing 50% of fat up to the age of 9 weeks and 6 months, respectively. The control group received a diet with 3% of fat. The fat consisted of lard (1/3) and sunflower oil (2/3). Serum cholesterol was determined according to the standard method 1 of the DAB 7 (German Pharmacopoeia); liver cholesterol was estimated by the method of Naito and Lewis. As compared to the control animals, the 9-week-old rats on the high-fat diet showed serum cholesterol values (total, free and esterified cholesterol) which were significantly lower. There was no difference in serum cholesterol level between the 6-month-old rats on the high-fat diet and the control animals. In contrast to this, the liver cholesterol levels of the 9-week-old and the 6-month-old rats on the high-fat diet were significantly increased. In both age-groups the ratio of free cholesterol to esterified cholesterol was changed in favour of the esterified cholesterol. The present results confirm the findings reported in the literature, except for the unchanged serum cholesterol values observed by the authors in the long-time dietary experiment.

Influence of dietary fat saturation on lipid absorption in the rat

Flux (mumole/h) of triglycerides, phospholipids and cholesterol into the thoracic duct lymph was measured in rats receiving a constant intraduodenal infusion of a cholesterol-free oil rich in either polyunsaturated (P/S = 4.8) or saturated (P/S = 0.2) fatty acids. Rats had ad libitum access to a fat-free semi-synthetic diet throughout the experiment. Oils were infused at a rate equivalent to a 10% (w/w) fat-containing diet for at least 18 h prior to collection of lymph; both oils were compared in each animal. Although absorption of the infused oils approximated 100%, triglyceride flux was significantly lower during infusion of the saturated compared to the polyunsaturated oil. Phospholipid and total cholesterol fluxes were not significantly affected by the type of oil, but the percent of lymph total cholesterol which was esterified was slightly but significantly lower during infusion of the unsaturated oil. Using the molar phospholipid/triglyceride ratio as a index of lymph lipoprotein size, it was found that absorption of the oil rich in polyunsaturated fatty acids resulted in an increase in the mean size of lymph lipoproteins. The potential significance of an influence of dietary fat saturation on lymph lipoprotein size and cholesterol esterification for the ultimate metabolic fate of absorptive lipoprotein constituents is discussed.

Type and amount of dietary fat affect relative concentration of cholesterol in blood and other tissues of calves

Sixteen male Holstein calves consumed by nipple a reconstituted milk containing nonfat dry milk and either soybean oil or tallow for 24 weeks. Calves fed milk in this manner (with no dry feed) are functionally nonruminants because the milk bypasses the ruminoreticulum. The fat in these diets contributed about 30% of total dietary calories. The calves consuming soybean oil milk had significantly greater amounts of cholesterol in blood plasma and adipose tissue than did the calves consuming tallow milk.

Type and amount of dietary fat affect relative concentration of cholesterol in blood and other tissues of rats

The effects of diet on tissue cholesterol disposition in the rat were studied. Growing rats were fed a nonfat dry milk supplemented with two levels of soy-bean oil (SBO) and tallow (T) such that either 30% or 50% of total dietary calories came from fat. Two of four groups of rats fed the diets with 50% of calories from fat were supplemented with 20% ground whole oats. Considering all diets, rats fed SBO had higher blood and kidney cholesterol than did rats fed T; supplementation of the diet with oats increased the plasma cholesterol of the "50%" SBO rats and , conversely, decreased plasma cholesterol of the "50%" T rats. Muscle cholesterol content was not affected by variations in dietary fat and oats. In all treatments, cholesterol concentration of epididymal fat and liver were greater in the SBO-fed than in the T-fed rats.

Effect of unsaturated lipids on the bile flow and biliary excretion of cholesterol and bile salts in rats

When rats were fed safflower oil or coconut oil for 30 days, or soyalecithin (EPL) or egg phospholipids for 7 days, the rates of bile flow, concentration of cholesterol in the bile as well as unsaturation in the biliary phospholipids were markedly higher in the animals receiving the more unsaturated lipids. It is concluded that feeding of lipids containing polyunsaturated fatty acids effects an increase in the unsaturation of the biliary phospholipids and thereby causes increased excretion of cholesterol through the bile.