AbstractThe continued suggestion that the ratio of saturated to unsaturated acids in the diet can influence the general health of a mammal is still not easily explained at a biochemical level. Studies on the metabolism of glycerophosphatides show that the enzymes involved appear to differ in the degree of selectivity toward substrates with different amounts of unsaturation. In general, each individual acid will have its own characteristic metabolic fate. The acyl‐CoA:acyl‐GPC acyltransferases have a marked specificity for both the position to be acylated and the particular acyl‐CoA involved. In some cases, the observed distributions of fatty acids in naturally occurring lecithins and triglycerides are similar to the distributions predicted from in vitro studies of the acyltransferase enzymes. Other enzymatic steps, such as acid activation and N‐methylation, can also be shown to influence the fatty acid composition of the glycerolipids. The relative importance of these metabolic processes must now be determined.