Effects of different dietary intake of essential fatty acids on C20∶3ω6 and C20∶4ω6 serum levels in human adults

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Abstract
Four diets which differed in fatty acid composition were provided for five months each to a group of 24 healthy nun volunteers. The diets contained 54% carbohydrates, 16% proteins and 30% lipids. One-third of the lipid part remained unchanged during the whole study, and two-thirds were modified during each period. For this latter portion, one of the following dietary fats was used: sunflower oil, peanut oil, low erucic acid rapeseed (LEAR) oil or milk fats. This procedure allowed an evaluation of the effects of various amounts of dietary linoleic acid (C18∶2ω6) and alpha-linolenic acid (C18∶3ω3) on the serum level of their metabolites. A diet providing a large amount of linoleic acid (14% of the total caloric intake) resulted in low levels of dihomo-gamma-linolenic acid (C20∶3ω6) and arachidonic acid (C20∶4ω6) in serum phospholipids and cholesteryl esters. A diet providing a small amount of linoleic acid (0.6% to 1.3% of the total caloric intake) induced high levels of ω6 fatty acid derivatives. Intermediate serum levels of C20∶3ω6 and C20∶4ω6 were found with a linoleic acid supply of about 6.5% of the total caloric intake. Serum levels of ω6 metabolites were not different after two diets providing a similar supply of C18∶2ω6 (4.5% to 6.5% of the total caloric intake), although in one of them the supply of C18∶3ω3 was higher (1.5% for LEAR oil versus 0.13% for peanut oil). Under our experimental conditions (healthy human adults fed on a normo-caloric diet with 30% lipids), we tried to determine PUFA (linoleic and linolenic acid) allowances which should be recommended for adults. The aim of the study was to obtain a hypocholesterolemic or normocholesterolemic effect while keeping normal 20∶3ω6 and 20∶4ω6 serum levels which would evidence a normal linoleic acid metabolism. The amounts recommended are: linoleic acid 5 to 6% of the total calories; alpha-linolenic acid 0.5 to 1% of the total calories.