UNSATURATED FATTY-ACID BIOAVAILABILITY IN GROWING RATS FED LOW OR ADEQUATE PROTEIN DIETS WITH SUNFLOWER OR SOYBEAN OILS

The relationship of serum very low density lipoproteins (VLDL) to hepatic lipid composition was studied after 28 days of protein depletion to determine the interactions between dietary protein levels and the essential fatty acid (EFA) availability. This was examined in rats using a dietary combination of 20% or 2% casein with 5% vegetable oils, variable in their n-6:n-3 fatty acid ratios. Rats were divided into four groups, SFC (20% casein + 5% sunflower oil); SFd (2% casein + 5% sunflower oil); SC (20% casein + 5% soybean oil); Sd (2% casein + 5% soybean oil). Dietary protein depletion decreased phospholipid and protein concentrations in liver and VLDL, whereas triacylglycerol amounts were enhanced in liver, but lowered in VLDL. Dietary protein depletion strongly depressed VLDL apolipoproteins. Protein-deficient groups (SFd and Sd) exhibited, in both liver and VLDL, decreased linoleic acid in triacylglycerol fractions and depressed both arachidonic and linoleic acids in phospholipid fractions. In spite of short periods of dietary treatment, protein depletion involved an impairment in EFA availability. Total n-6 polyunsaturated fatty acids contents were diminished in liver and VLDL lipids, while total n-3 polyunsaturated fatty acids contents were diminished in only VLDL triacylglycerol and phospholipid. Furthermore, sunflower oil amplified this impairment, and the lack of alpha-linolenic acid involved a greater diminution in n-3 polyunsaturated fatty acids and enhanced 20:3 n-9 and 22:5 n-6, especially in phospholipid fractions. In this experiment, in spite of a short period of dietary treatment, protein depletion strongly impairs EFA metabolism and accentuates the alpha-linolenic acid deficiency.