Soy: Benefits and Drawbacks

I got a request this week to do a post on the Pros and Cons of eating soy. (Yay for requests!!!)

Here’s the short story: traditional ways of preparing soy, such as miso, tempeh, and soy sauce, which slow-ferment the mature soybean, are generally good. But the modern, Western, over-consumption of soy (which is generally processed by crushing instead of fermenting) may have harmful effects, largely due to the estrogenic effects of soy isoflavones and the harmful omega-6 fatty acids in soybean oil.

Sadly, most of us living in Western cities can’t even easily access traditionally fermented soy products – the soy sauce most people buy here has likely been quick-processed instead of slow-fermented.

My non-expert recommendation: drink whole, organic cow’s milk if you’re Northern European and evolved to digest it; buy your soy sauce, natto, miso, and tempeh from raw foods and health foods stores that vet their brands for whole and traditional production methods (“nama shoyu” is usually the name for a traditional, raw, fermented soy sauce that was not sped along by heat); and if you’re lactose intolerant, get your calcium from yogurt, greens (like spinach, collards, broccoli, kale, and chard), sesame seeds or tahini, seaweeds like kelp, almonds, papaya, flax seeds, and nut milks, like almond, hazelnut, or cashew milk, or fortified rice milk.

Here’s the long story:

The nutritional profile of the soybean is healthful.

Soy is high in protein, lecithin and vitamin E, and has little saturated fat and no cholesterol. It can be digested by people who are lactose intolerant, making calcium-fortified soymilk a good substitute for cow’s milk, and by people who are allergic to the protein in cow’s milk (casein). Studies reported in the New England Journal of Medicine and the American Heart Association found a positive correlation between soy intake and significant decreases in serum cholesterol, LDL (bad cholesterol), and triglyceride concentrations, most likely because soy products are high in polyunsaturated fats, fiber, vitamins, and minerals and low in saturated fat, and subjects in the study were using soy foods to replace animal protein high in saturated fat and cholesterol. (1995 New England Journal of Medicine vol. 333: 5; January 2006 American Heart Association review in the journal Circulation.)

But the phytoestrogens in unfermented soy have estrogenic effects on humans, and it’s generally not a good thing to introduce exogenous hormones into the body. Phytoestrogens are plant estrogens; the isoflavones in soybeans are estrogenic.

A 2008 study of 99 men who attended a fertility clinic with their partners between 2000 and 2006 concluded that men who consume an average of half a portion of soy products per day are more likely to have a lower concentration of sperm, particularly if they are overweight or obese (body fat produces estrogen). Professor Richard Sharpe, head of the Medical Research Council's human reproductive sciences unit at Edinburgh University, recently completed studies on the effects of soy milk on young male monkeys, which showed that it interferes with testosterone levels. The UK food standards agency, because of concerns over the development of infants, recommends avoiding introducing soy formula or soy products until an infant is over 12 months of age (unless absolutely necessary – e.g., the mother can’t breastfeed and the child can’t tolerate cow’s or goat’s milk).

I myself have sensitivity to the estrogen in soy products and was advised in 2002 to cut them out of my diet by a dermatologist and family friend who noticed that I was getting a skin rash that he was seeing frequently in 20-something women who, out of health consciousness, consumed a lot of soy products. (I still use nama shoyu in small quantities and will occasionally have some broiled, miso-marinated fish; I haven't seen the skin rash recur since I cut all other soy products out of my diet.)

So why have Asian populations, which have consumed soy-rich diets for 5,000+ years, not shown any signs of reduced fertility or other health problems?

It all goes back to Michael Pollan, who touts traditional food cultures and lambasts Western food industrialization: the way Asian cuisines traditionally used the soybean is nothing like the way we in the West have encountered it since World War II.

Soy, like corn, has become a darling of the food industry, and is used in almost every processed food product in myriad ways never before tried by traditional food cultures. Soy is in 60% of all processed food, as soy flour, hydrolyzed vegetable protein, soy protein isolate, protein concentrate, textured vegetable protein, soybean oil, or soy lecithin.

Traditional Asian soy products did not include soymilk (which was made as a precursor to making tofu, but not for drinking) or edamame, and what was consumed had usually been naturally fermented anywhere from several months to more than a year. Traditional fermentation, using natural whole ingredients and slow aging, reduces isoflavone levels. Sadly, modern industrially processed soy products, such as soy sauce and miso, short-cut the natural fermentation process by crushing raw beans; extracting the oil; toasting and grinding the meal; cleaning, bleaching, degumming, and deodorizing it; then fermenting at high temperatures for three to six months. It seems also that modern American strains of soy have significantly higher levels of isoflavones than Japanese or Chinese ones because of breeding for pest-resistance.

As to soy and health risk, according to the Mayo Clinic:

1. The jury is out on the all of the following:
- whether dietary soy or soy isoflavone supplements increase or decrease the risk of breast, uterine, or prostate cancer;
- whether dietary soy or soy isoflavone supplements are beneficial, harmful, or neutral in cancer patients; and
- whether soy isoflavones reduce post-menopausal “hot flashes” in women.

2. It has been suggested that soy supplements might allow tuberculosis patients to take higher doses of antimicrobial drugs safely.

3. Soy does not appear to cause long-term toxicity.

4. Studies on animals suggest that eating raw soybeans or soy flour/protein powder made from raw, unroasted, or unfermented beans may cause damage to the pancreas.

5. Patients with hormone-sensitive cancers, such as breast, ovarian, or uterine cancer, and other hormone-sensitive conditions, such as endometriosis, are discouraged from eating soy because of its estrogen-like effects.

Further reading:

Giampietro PG, Bruno G, Furcolo G, et al. Soy protein formulas in children: no hormonal effects in long-term feeding. J Pediatr Endocrinol Metab 2004;17(2):191-196.

Hunter, B.T.  The downside of soybean consumption.

Izumi T, Saito M, Obata A, et al. Oral intake of soy isoflavone aglycone improves the aged skin of adult women. J Nutr Sci Vitaminol (Tokyo) 2007 Feb;53(1):57-62.

Koo WW, Hammami M, Margeson DP, et al. Reduced bone mineralization in infants fed palm olein-containing formula: a randomized, double-blinded, prospective trial. Pediatrics 2003;111(5 Pt 1):1017-1023.