Benefits of Soy Protein

Soy protein is very healthy: it is very low in fat, contains no cholesterol and contains phytochemicals. The main phytochemicals in soy protein are isoflavones, saponins and phytc acid. These phytochemicals are strong antioxidants but have many other properties. Soy protein and its associated phytochemicals seem to reduce heart disease, osteoporosis and risk of cancer.

Soy Protein and Heart Disease

Soy protein reduces the cholesterol and help to reduce the risk of heart disease. The most important scientific study about the relationship of soy protein intake and heart disease is the meta-study by Anderson et al (Meta-analysis of the effects of soy protein intake on serum lipids. N Engl J Med 1995;333:276-282). They concluded that the consumption of soy protein rather than animal protein significantly decreased serum concentrations of total cholesterol, LDL cholesterol, and triglycerides without significantly affecting serum HDL cholesterol concentrations.
Anthony MS et al found that isoflavones in soy protein improve cardiovascular disease risk factors without apparent deleterious effects on the reproductive system of peripubertal rhesus monkeys (Soybean isoflavones improve cardiovascular risk factors without affecting the reproductive system of peripubertal rhesus monkeys. Journal of Nutrition 1996;126:43-50).
Erdman, J.W et all recommend in their study (Soy protein and cardiovascular disease: A statement for healthcare professionals from the nutrition committee of the AHA. Circulation 2000;102(20):2555-9) that including soy protein in a diet low in saturated fat and cholesterol promotes heart health. They found that the daily consumption of more than 25 g soy protein, with its associated isoflavones, could improve lipid profiles in hypercholesterolemic humans. They also found that soy protein without the isoflavones appears to be less effective in preventing heart disease. Taking isoflavones supplements without soy protein does not lower cholesterol but may provide other cardiovascular benefits.

Soy Protein and Osteoporosis

Research suggests that consuming soy protein and the replacement of animal protein with plant protein may protect against osteoporosis. Although Japanese women consume less calcium than most Western women do they have a lower prevalence of fractures. This could be explained by the soy protein consumption of Japanese women. Alekel, D.L. et al found that soy isoflavones attenuated bone loss from the lumbar spine in perimenopausal women.
Source: Isoflavone-rich soy protein isolate attenuates bone loss in the lumbar spine of perimenopausal women. Am J Clin Nutr 2000;72(3):844-52.

Soy Protein and Abdominal Body Fat

Soy protein contains calories, about 4 kcal per g, but does its consumption increase our body fat? Of course, if you add extra soy protein to your diet you may expect weight increase, but how does soy protein compare with for example dairy protein. One study investigated the effect of a daily supplementation of soy protein or dairy protein on body fat of postmenopausal women [1]. The researchers found that the group who consumed soy protein lost abdominal fat (-12 ml), whereas the group who had the soy protein replaced with dairy protein (casein) showed an increase in abdominal fat (+39 ml). Other parameters, such as total body fat, insulin secretion and lean mass did not differ between the groups. This study concluded that a daily supplementation of soy protein prevents the increase in subcutaneous and abdominal fat, observed with an isocaloric casein placebo in postmenopausal women.
Source: Effect of a daily supplement of soy protein on body composition and insulin secretion in postmenopausal women. Fertil Steril. 2007 Dec;88(6):1609-17.

Soy Protein and Cancer Risk

Epidemiological studies suggest that soy protein may reduce the risk of certain cancers, including breast cancer and prostate cancer. Japanese women, who eat a lot of soy protein (mainly from soy tofu and miso), have a much lower risk of breast cancer or prostate cancer than Western people have. The anti-cancer effect of soy protein could be explained by the phytochemicals, which are associated with the soy protein. These phytochemicals include the isoflavones genistein, daidzein and glycitein, phytic acid, saponins and protease inhibitors. Isoflavones and phytic acid have strong antioxidant properties and can prevent oxidative damage by free radical to our DNA and cells. Shu X.O. et all suggest that high soy intake during adolescence may reduce the risk of breast cancer in later life (Soyfood Intake during Adolescence and Subsequent Risk of Breast Cancer among Chinese Women. Cancer Epid Biomarkers Prev. 10: 483-488). The inverse association between soy protein intake and reduces risk of breast cancer was observed for each group of soyfoods examined.