Is Soy Healthy?
Soy products such as fresh or frozen soybeans (edamame), tofu, soy nuts, and some soy burgers can be beneficial to heart health when they displace foods such as hamburgers, cheese and other sources of saturated fat from the diet, however the provide very little advantage of other complete proteins, such as whey, casein, egg and lean poultry sources. Recent clinical trials have shown that consumption of soy protein compared to other proteins, such as those from milk or meat, can lower total and LDL-cholesterol levels however these scientific studies show that 25 grams of soy protein daily in the diet is needed to show a significant cholesterol lowering effect.
Things to consider when choosing soy as a protein source:
- Soy contains a group of protease inhibitors that can inhibit the digestion of protein by interfering with the activity of two important enzymes, trypsin and chymotrypsin. Protease inhibitors interfere with cell communication, protein metabolism and cell growth and may inhibit normal growth and repair functions in children. At first the soy industry claimed that these inhibitors were destroyed by cooking, but that has been disproved. Protease inhibitors have been shown to survive cooking and processing to a small but significant degree Certainly significant for a small child. On a good note, this action may produce an anti-cancer effect in humans by interfering with the growth and spread (metastisis) of tumors.
- Soy has high concentrations of certain chemicals that combine with essential minerals to deposit insoluble salts difficult for your kidneys to eliminate.
- Excessive soy consumption may inhibit brain repair functions. A study with Japanese-Americans found a disturbing correlation between soy consumption and cognitive impairment (refer to:[v] 2. White LR, Petrovitch H, Ross GW, Masaki KH, Hardman J, Nelson J, Davis D, Markesbery W, Brain aging and midlife tofu consumption. J Am Coll Nutr 2000 Apr;19(2):242-55).
- There are studies that suggest a causal relationship between soy phytoestrogens and early puberty in girls and delayed physical maturation in boys.
- Two components of soybeans (eg genistein and daidzein) have estrogen-like activity in humans and animals, which is not necessarily a good thing, especially for prepay women and the fetus. (refer to: Soy Infant Formula Could Be Harmful to Infants: Groups Want it Pulled. Nutrition Week, Dec 10, 1999;29(46):1-2). A study published in the British medical journal, Lancet found that infants fed soy formula had levels of phytoestrogens that were 13000-22000 times higher than natural estrogen concentrations in early life. High doses of the phytoestrogens genistein and daidzein have also been found to interfere with thyroid function and while this would have no effect on a person eating a varied diet, those using soy as their primary source of protein may suffer, even to the point of thyroid disease.
Bottom Line on Soy and Health
Eaten in moderation soy’s benefits, especially if replacing meat that is high in saturated fats, probably outweigh the risks, however, care should be employed by sensitive populations (pregnant women, children, etc.) when choosing soy as a staple in the diet.