I acquired more knowledge as I read The Vegetarian Myth by Lierre Kieth, for the purpose of my Paleo and Sustainability post. The book has long since been returned to the library, so I'm going off of memory, but I think you'll be alarmed by what you read below.
Historically, soybeans were used as a cover crop in Asian cultures. The plant was only eaten in small amounts, and it was heavily fermented into miso or tempeh and eaten with nutrient- and mineral-rich fish broth, which somewhat neutralized the toxins in the soy.
Soy exhibits all the problems of legumes, which I discuss in my principles of paleo post, and then some. Soy contains the usual paleo suspects of anti-nutrients, which bind to vitamins and minerals and prevent absorption by the body; as well as saponins, which damage your intestinal lining. As if that's not bad enough, due to its unique characteristics and also because of its high levels of consumption as a modern dietary staple, soy goes far beyond these issues. First, soy is a goitrogen, and can (sometimes permanently) damage your thyroid. This has been observed widely among Asian cultures, as well as infant populations fed soy formula. Second, soy has phytoestrogens, which lock onto estrogen receptors in the body as well as block the production of estrogen. Phytoestrogens result in reproductive failure along with a host of other hormonal problems. According to Keith, there are hundreds of plants that contain phytoestrogens; soy is the only one humans eat.
The prominence of soy in vegetarian diets, along with other nutritional deficiencies, may play a significant role in the menstrual problems suffered by vegan women. In one study cited in The Paleo Answer, 78 percent of women put on a vegetarian diet stopped menstruating within 6 weeks. Keith cites similar studies linking soy to infertility, notes side-effects similar to birth control pills, and references her own experiences while on a vegan diet.
Keith also accuses soy of harming men's reproductive health, but only points to animal studies. This is shaky ground, so I won't go into any more detail here. But the fact that monks have historically eaten soy in order to reduce their sexual urges, provides enough evidence for me to steer clear.
Soy has been shown to cause accelerated brain aging, reduced cognitive ability, and a heightened risk for Alzheimer's disease.
Soy-based infant formula is deficient in several key nutrients, and results in poor health and potentially permanent reproductive problems. Keith discusses how, due to successful marketing efforts and low-bid government contracts, children in the poorest populations both in the US and abroad receive the highest doses of these toxic soy formulas.
What about the theory that soy can reduce the risk of breast cancer? What about prevention of osteoporosis? According to Keith, these are the result of Big Ag twisting research to bolster unproven theories, and attempting to link together unproven hypotheses.
Lastly, almost all soybeans today are genetically modified, and if that's not enough, soy-based foods (from soymilk to that yummy-looking vegan "pepperoni pizza" in the frozen food aisle) are some of the most heavily processed frankenfoods the industry has synthesized to date. These features alone make soy a very fitting sort of paleo antichrist.
|My mouth is watering|
Even prominent vegan nutrition gurus steer clear of soy, including Brendan Brazier, the author of Thrive. This should provide encouragement to vegetarians and vegans who have made soy the mainstay of their diet.
Since learning all this about soy, I've certainly begun monitoring the ingredients lists of the foods I eat. I've found that -- almost without exception -- if it's processed, then it contains soy. Before paleo, my day sometimes consisted of Kashi Go-Lean cereal in the morning, a Clif Builder's bar as a snack, a tofurkey sandwich, and then some steamed edamame after they gym. I've cut most of this out, but still enjoy a Clif bar during a bike ride once in a while.
Full disclosure, of course: there is plenty of dispute in the nutritional world on soy. Just google "soy problems" and you'll see plenty of experts touting the benefits of soy, along with a slew of indictments. Based on what I've read and what my body tells me, I try to avoid soy at every turn.