Impact of Dietary Protein on Polyunsaturated Fatty Acid Desaturation in Rats Fed Diets Rich in α-Linolenic Acid

Delta 6-desaturase activity and fatty acid composition of liver microsomes were measured periodically in rats fed diets high in α-Iinolenic acid (perilla oil) containing either casein (CAS) or soybean protein (SOY) as a protein source. Delta 6-desaturase activity measured by using linoleic· acid as a substrate (18: 2n-6→18: 3n-6) and the linoleic acid desaturation index as estimated by the (20: 3+20: 4)/18: 2 ratio in microsomal phospholipids were significantly higher in rats fed the CAS diet than in those fed the SOY diet at days 4 and thereafter. The proportion of eicosapentaenoic acid (20: 5n-3) was also significantly higher in the CAS group than in the SOY group. These results confirmed a differential impact of the dietary protein type on the metabolism of polyunsaturated fatty acids even when rats were fed fat rich in α-Iinolenic acid.