Abstract
Dietary protein affects not only the metabolism of cholesterol, but also that of linoleic acid and triglyceride. Soy protein, as compared with casein, reduced the conversion of linoleic acid to arachidonic acid, and hence the production of eicosanoids, in rats. One of the mechanisms of the soy protein-dependent decrease of linoleic acid desaturation was considered to be a homeostatic response that compensates for an increase of hepatic microsomal membrane fluidity, caused by a decrease of the microsomal cholesterol/phospholipid ratio. Also, the protein-dependent effect could be at least due to aspects of amino acid composition, such as arginine content. On the other hand, dietary soy protein, as compared with casein, reduced the serum and liver triglyceride concentration and white adipose tissue weight in rats. Also dietary soy protein increased hepatic fatty acid β-oxidation. Recently, it has been shown that dietary conjugated linoleic acid (CLA) reduces adipose tissue weight. It can be considered that the body fat-reducing effect of dietary CLA becomes more significant in combination with soy protein than with casein.
