Triglycerides containing similar amounts of essential fatty acids (EFA) (approximately 53% of the total fatty acids) but different fatty acid configurations on the glycerides were prepared from soy bean oil and fat from a pig fed on a 20% safflower oil ration. The vegetable oil contained approximately 48% of the total EFA at the 2-position, while the pig fat contained only 27% at this locus. Diet containing 5% (w/w) soy bean oil or pig fat were supplied ad libitum to two groups of male weanling rats for 3, 6 and 13 weeks. After these periods there was no difference in the concentration of plasma cholesterol in the two groups. The liver cholesterol level tended to increase when rats received pig fat for longer periods. In the group receiving pig fat, addition of 1% cholesterol to the diet resulted in a considerable increase in the plasma and liver cholesterol levels and the ratio of esterified to total cholesterol in the liver increased to above that in the group receiving vegetable oil plus cholesterol. These data suggest that the effect of dietary EFA on the metabolism of cholesterol differs with the position of the esterified EFA on the glyceride. Thus, EFA at the 1- and 3-positions on triglycerides may have less effect in lowering the cholesterol level than EFA at the 2-position, particulary when cholesterol is ingested simultaneously.
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Yamamoto et al. (1969) studied this question.