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Soy protein and hyperlipidemia

Hyperlipidemia is the condition of abnormally elevated levels of lipids in the bloodstream. These lipids include cholesterol, cholesterol esters, phospholipids and triglycerides. Previous research have shown that soy protein reduces triglycerides by 12% compared to animal protein. Retinoic acid is a metabolite of vitamin A and plays an important role in lipid metabolism. It binds to retinoic acid receptors and modulates pathways associated with many types of carcinogenesis. Retinoids are used as treatment for certain types of cancer but have serious side effects, such as the induction of hypertriglyceridemia. Soy protein isolate has been shown to reduce the severity of retinoic acid induced hypertriglyceridemia in rats.
Xiao and co-workers at the Banting Research Centre, Ottawa, were the first to investigate the effect of alcohol-washed soy protein isolate (very low levels of isoflavones) and isoflavones on retinoic acid receptor gene expression and DNA binding activity in rats. They found consumption of the soy protein isolate dose-dependently increased the beta2 isoform of retinoic acid receptor protein in both male and female rats. Supplementation with additional isoflavones had no consistent additional effect. The exact mechanism by which soy protein isolate increases this protein level is not know, but the scientists suggest that the higher arginine-to-lysine ratio of soy protein or a bioactive peptide may play a role.

The study concluded that dietary soy protein may reduce retinoid-induced hypertriglyceridemia by affecting hepatic retinoic acid receptor beta2 protein content and retinoic acid receptor beta DNA binding activity.

Source: Dietary soy protein isolate modifies hepatic retinoic acid receptor-beta proteins and inhibits their DNA binding activity in rats. Journal of Nutrition. 2007 Jan;137(1):1-6.


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