Composition of lipids in human serum and adipose tissue during prolonged feeding of a diet high in unsaturated fat

Elderly institutionalized men were assigned at random to two groups, one of which received a conventional diet while the other was fed a diet in which the major modification was substitution of unsaturated for saturated fat. Changes in serum lipids and in adipose tissue over periods up to 5 years are described. In control subjects, mean serum cholesterol rose 4% over the first 20 months, then fell during the next 40 months to a level 10% below the starting concentration. In the experimental group there was an immediate drop, followed by further changes roughly parallel to those in the control subjects. The mean difference between the control and experimental groups was 14.0% of the starting level. Changes in serum total lipid were similar, but the percentage difference between control and experimental groups was only 6.8% of the baseline level. All major esterified serum lipid fractions of experimental subjects contained increased concentrations of linoleic acid. This was most marked in triglyceride, which at 3 years had a composition similar to that of the dietary fat in both groups of subjects. Adipose tissue linoleic acid rose in men on the experimental diet from 11% of total fatty acid at time zero to 32% at 5 years. The rise could be fitted to an exponential function with a half-time of 680 days. The rate of rise during the 1st year was correlated negatively with initial body weight and positively with weight gain; the influence of adherence to the diet was much less pronounced.

Influence of a diet high in unsaturated fat upon composition of arterial tissue and atheromata in man

Detailed chemical analyses have been carried out on aorta, and on coronary and aortic atheromata, of men who died during a study of prolonged use of diets rich in unsaturated fat and of control subjects. Concentrations of total aortic lipid and of total aortic calcium were not significantly different for the two groups of subjects. Concentrations of cholesterol and cholesterol esters, triglyceride, and phosphatide showed no difference between the two groups in analyses of aorta, uncomplicated aortic atheromata, complicated aortic atheromata, and coronary atheromata. Coronary atheroma lipid contained substantially more triglyceride than did aortic atheroma lipid, whether derived from complicated or uncomplicated plaques.

Atheroma triglyceride in experimental subjects contained more linoleic acid than in control subjects, in all types of plaques. Lesser but significant increases in linoleic acid were seen in cholesterol ester and phosphatide of coronary atheromata and complicated aortic atheromata. In the case of uncomplicated aortic atheroma, changes in linoleic acid of cholesterol ester and phosphatide were smaller and not significant. In both groups of subjects, coronary atheroma contained more cholesteryl oleate and less linoleate than did aortic atheroma.

Linoleic acid contents of atheroma lipid fractions were positively correlated with the linoleic acid figures for corresponding fractions of the most recent antemortem serum samples. Ratio of linoleic acid in an atheroma lipid fraction to the linoleic acid content of the corresponding serum fraction was, in most cases, constant after the time of the first sample, obtained after 495 days on experimental diet. It is postulated that this ratio constitutes an estimate of the fraction of atheroma fatty acid derived from plasma. In cholesterol ester and triglyceride, the ratio was about 0.65 in experimental subjects, higher in subjects on the control diet. The ratio for phosphatide was about 0.5 in both groups of subjects.