Dietary protein influences polyunsaturated fatty acid patterns of rat tissue lipids

Casein (CAS) promotes desaturation of linoleic acid (LA) in relation to soybean protein (SOY). This protein-effect could be detected within 4 days after feeding different proteins, and persisted even after overnight fasting. The difference was found irrespective of dietary fat even when delta 6-desaturation was depressed by alcohol consumption. The aortic production of prostacyclin (PGI2) was higher in the CAS group than in the SOY group irrespective of alcohol consumption. When the effect of lysine/arginine (Lys/Arg) ratio of dietary protein on LA desaturation was studied, the addition of Arg to CAS resulted in trend for the proportion of LA to increase and a arachidonic acid (AA) to decrease in liver phosphatidylcholine (PC). However, the effect of Lys addition was inconclusive. Thus, the content of Arg rather than the Lys/Arg ratio was at least one of the factors for the protein-dependent effect.