Total plasma cholesterol, from diets

Monounsaturated fats Triacylglycerols containing primarily fatty acids with one double bond are referred to as monounsaturated fat. Unsaturated fatty acids are generally derived from vegetables and fish. When substituted for saturated fatty acids in the diet, monounsaturated fats lower both total plasma cholesterol and LDL cholesterol, but increase HDLs. This ability of monounsaturated fats to favorably modify lipoprotein levels may explain, in part, the observation that Mediterranean cultures, with diets rich in olive oil (high in monounsaturated oleic acid), show a low incidence of coronary heart disease. 

The evaluation of effects of dietary constituents on plasma lipid and lipoproteins requires selective measurements of individual lipoprotein classes. For example, the addition of cholesterol to the diet in the rat does not increase total plasma cholesterol levels in the present study a slight reduction in plasma cholesterol was in fact seen. However, the HDL cholesterol fraction was markedly reduced, and the VLDL and/or LDL cholesterol level must therefore have been increased. Extrapolation from data in humans would indicate that this shift in lipoprotein profile is disadvantageous from the atherogenic point of view. The increase in VLDL/ LDL cholesterol may readily be explained by the dietary load of cholesterol which is transported to peripheral tissues by these lipoprotein particles (J6). The reduction in HDL which are considered to be involved in cholesterol transport from peripheral tissues to the liver, is however an interesting but so far unexplained phenomenon. 

A positive effect of phytosterols from taU oil phytosterols showed a dramatic protection against atherosclerosis in mice (101). Mice fed a cholesterol-enriched diet containing a phytosterol mixture exhibited reduced plasma cholesterol levels and decreased formation of atherosclerotic lesions. In humans, phytosterol treatment resulted in an average of 10% reduction of total cholesterol and a 13% reduction in LDL-c (102). 

A typical American diet contains about 40% of its total energy content as fat. About half this energy is in the form of saturated fatty acids, one-fourth as monounsatu-rated fatty adds, and one-fourth as polyunsaturated fatty adds (PUFAs) (Ginsberg et dl., 1990). The quantity and nature of dietary fats carx influence the lex. d of plasma cholesterol. A reduction in total fat from the typical 40% of energy intake to 30% can result in a decrease in plasma cholesterol. 

Cholesterol is supplied by absorption from diet (0.3-0.5 gfday in human) and biosynthesis (1.0-1.2 g/day) and is excreted mainly as bile acids into feces (0.8-1.3 g/day) (8). To reduce body cholesterol, three major strategies can be considered (a) inhibition of cholesterol absoipticm by a compound such as sitosterol, (b) inhibition of bile acid reabsorption by a compound such as cholestyramine, and (c) inhibition of cholesterol biosynthesis. Since more chan 70% of the total input of body cholesterol in humans is derived from de novo synthesis, it is expected that plasma cholesterol levels can be reduced by inhibition of cholesterol biosynthesis. 

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