Abstract
1. Lipids exist in the blood serum as emulsions ("chylomicrons") and as solutions of lipoprotein containing proteins, cholesterol, and other lipids. Interest in relation to atherosclerosis is centered on the cholesterol and the beta lipoproteins which contain most of the cholesterol.
2. The diet influences the blood lipids in man and animals but great quantitative differences between species makes it essential to study man himself to discover the effects of the diet on the blood lipids in man.
3. The amount of lipid in the chylomicron form in the serum is practically independent of the concentration of cholesterol and lipoproteins in the serum. The correlation between the concentrations of alpha and beta lipoproteins is very low.
4. Experiments on man show that dietary cholesterol per Se, even in large amount, has no important influence on the serum cholesterol concentration but that the latter is markedly affected by the total fat content of the diet.
5. Calorie intake per se has little influence on the blood lipids. Such effect as it has may be secondary to fat metabolism differences commonly associated with differences in calorie intakes.
6. Studies on population samples of healthy men show a marked direct relationship between the content or proportion of fat in the diet on the one hand and the concentration of total cholesterol and of beta lipoproteins in the serum on the other. The effect of the diet tends to be greater in middle-aged men than in younger men.
7. The average concentration of cholesterol in the serum of men in areas where the diets are very high in fats (of the order of 40 per cent of calories), is 25 to 50 per cent greater than the average in areas where the diets are low in fats (of the order of 20 per cent, or less, of calories).
8. A significant effect of dietary fat level on the serum cholesterol concentration is evident in man in a few weeks on a changed diet. The effect tends to increase very slowly with time thereafter and it is most pronounced when comparison is made between populations habitually subsisting on different diets.
9. It is not known how the dietary fat intake exerts its controlling influence on the blood lipids of man but the mechanisms must be complex.
Unavailability of liver triacylglycerol increases serum cholesterol concentration induced by dietary cholesterol in exogenously hypercholesterolemic (ExHC) rats
