Effects of a soy milk supplement on plasma cholesterol levels and oxidative DNA damage in men - a pilot study

Background: Phytoestrogens are a major component of Asian diets and may be protective against certain hormone-dependent cancers (breast and prostate) and coronary heart disease. They may also have antioxidant function in scavenging potentially harmful free radicals and thus decreasing oxidative attack on DNA. Aims of the study: A pilot study to determine the effects of a phytoestrogen supplement, in the form of soy milk, on plasma LDL and HDL cholesterol levels and DNA damage in men. Methods: Ten healthy men participated in the study and were assigned to one of three groups consuming I litre of either soy milk, rice dream (vegetable protein control) or semi-skimmed cow's milk (animal protein control) each day for 4 weeks. Results: The soy supplement caused significant increases in plasma genistein and daidzein concentrations despite considerable interindividual variation (P<0.001). Supplementation with soy resulted in a decrease in oxidative damage to DNA bases detected using the comet assay compared with controls (P<0.05). However, there was no significant effect of the soy supplement on plasma cholesterol or triglyceride levels in comparison with control groups. Conclusions: A 4 week soy milk supplementation in healthy volunteers does not alter serum cholesterol levels but can have a protective effect against oxidative DNA damage in lymphocytes.