NUTRISPEAK by Vesanto Melina and Brenda Davis
• Our September column on soy generated interest, letters and controversy. While considerable negative press about soy can be found on the internet and even in men’s magazines, typically these arguments can be traced to groups that promote animal-based diets, convincing some to steer clear of soy and jump on the anti-soy bandwagon. Whereas certain individuals should avoid or limit soy due to allergies or severe thyroid problems, for most, soy foods are safe, nutritious and potentially beneficial.
Soy has a long history of use throughout Asia and among vegetarians worldwide. Two of the healthiest, long-lived populations – the Okinawan Japanese and the Seventh-day Adventists in Loma Linda California – are frequent soy consumers. If soy were dangerous, its effects would be reflected in the health and longevity of these populations. Soy has been extensively researched and about 2,000 new studies on soy are released yearly.
Soy’s nutritional benefits are similar to those of other legumes although soybeans are higher in protein and fat and lower in carbohydrates. Soybeans derive about 25-38% of calories from protein, compared with about 20 to 30% for other legumes. Soy’s protein content and quality are similar to that of animal products and better than that of other legumes. While most legumes are low in fat (2 to15% of calories), soybeans derive about 40% calories from fat, similar to many animal products. However, soy oils contain beneficial, rather than damaging, components and are mainly polyunsaturated, including omega-3 fatty acids. Soybeans are rich in fibre, B-vitamins (niacin, pyridoxine and folic acid) and minerals (calcium, iron, magnesium and copper). Calcium is added to enriched/fortified soymilk and tofu is commonly set with calcium; both are particularly high. For many years, experts thought iron was poorly absorbed from soy, yet recent evidence suggests absorption is quite high. When consumed with vitamin-C-rich fruits and vegetables, iron absorption is further enhanced. Nutrient absorption is further improved when soybeans are soaked or fermented.
Soy for men
No reliable, clinical evidence exists showing that soy lowers serum testosterone or exerts estrogen-like effects in men. Whereas evidence continues to mount linking meat with chronic disease, evidence is growing that soy can protect against prostate cancer, kidney disease, cardiovascular disease and male pattern baldness. As indicated in our September column, the scares about soy for men originated from two case studies in which men consumed 14 to 20 servings/day of soy and subsequently developed temporary health problems. Problems vanished when balanced diets were resumed. In contrast, two recent meta-analyses found no effects of soy protein or isoflavones on male reproductive hormones. Three clinical trials assessed effects of soy on sperm and semen and observed no adverse effects.
Enjoy soy in its various forms. Organic – which also means GMO-free in Canada – and fermented – such as tempeh or miso – foods are great choices. At the same time, much of the research showing favourable effects of soy was done on populations eating mainly unfermented soy milk, tofu and edamame. Three to four servings/day is a reasonable amount for adults and up to two servings/day for children.