Effect of alpha-linolenic acid in the human diet on linoleic acid metabolism and prostaglandin biosynthesis.

The effect of dietary alpha-linolenic acid intake on linoleic acid metabolism and prostaglandin (PG) biosynthesis was investigated in two groups of six healthy females (25-32 yr). They were given isocaloric formula diets (FD) containing linoleic acid at a constant intake (4% of calories), with different amounts of alpha-linolenic acid: 0% (FD4/0), 4% (FD4/4), 8% (FD4/8) (group I) and 12% (FD4/12) or 16% (FD4/16) (group II); the diets were given for 2 weeks each. Comparing diet FD4/0 to FD4/16, enrichment of alpha-linolenic acid was greatest in cholesteryl esters (+6.8% in plasma, +7.1% in low density lipoproteins (LDL), +5.9% in high density lipoproteins (HDL)), less in phosphatidylcholine (+2.5% in plasma, +2.9% in LDL, +2.7% in HDL), and least in platelet lipids (+0.7%). The accumulation of alpha-linolenic acid was compensated by a decrease of oleic acid. Eicosapentaenoic acid (EPA), which was excluded from the diet, increased in all plasma lipids with augmented alpha-linolenic acid intake, indicating a chain elongation and desaturation of alpha-linolenic acid to EPA. However, even at the end of FD4/16, EPA was less than 2% of total fatty acids in all plasma lipids. Plasma linoleic acid levels were constant during all dietary regimes, according to the constant dietary intake of this fatty acid. No replacement of linoleic acid by alpha-linolenic acid could be observed. The percentage of arachidonic acid in all lipids was unaffected by alpha-linolenic acid intake. As arachidonic acid was not provided by the diet, it can be concluded that alpha-linolenic acid does not inhibit chain elongation and desaturation of linoleic acid to arachidonic acid in man.(ABSTRACT TRUNCATED AT 250 WORDS)