The effect of a fish diet on serum lipids in healthy human subjects

A cross-over study was done with 19 male and 23 female volunteers living in a monastery and a convent, respectively. The effect of a fat gish (mackerel) diet on the blood serum lipid composition was studied. As the normal diet of these volunteers was of the lacto-ovo-vegetarian type, a control diet in which the fish was replaced by full-fat cheese was used. Subjects consuming the fish diet had a daily uptake of polyunsaturated acids of the omega3 family of about 8 g; comparable amounts of linoleic acid were ingested with both diets. Both diets were consumed for a period of 3 weeks. Serum cholesterol was slightly but significantly (7.5%) lower and serum triglycerides considerably lower (35%) on the fish diet, whereas high density lipoprotein cholesterol increased slightly. Lipoprotein analysis showed a strong very low density lipoprotein decrease by the fish diet while, in the men, both low and high density lipoproteins increased. The fatty acid composition of serum lipids showed considerable differences; C20:5omega3 increased in all fractions and C22:6omega3 was found in the triglycerides and the phospholipids, but not in the sterol esters. These increases occurred chiefly at the expense of C18:1omega9 and, in particular, C18:2omega6, which indicates a replacement of omega6 by omega3 acids. Long-chain monoenoic acids which are abundant in the mackerel were not detected in any serum lipid fraction.