by Jonny Bowden, M.A., C.N.
Like so much that is controversial in the nutrition community, the case of soy says a lot about marketing, economics and the American propensity for getting our information in soundbites.
Do the words ‘controversy’ and ‘soy’ belong in the same sentence? At first blush it sounds like a contradiction. Virtually everyone in the dietary establishment has gotten on the soy bandwagon, and even some maverick iconoclasts such as Dr. Barry Sears have come aboard. We’re told that the isoflavones (plant-based compounds found in soy products) have unique, disease-fighting properties and that Asian women who eat large amounts of soy products have an easier time during menopause and have fewer hot flashes and mood swings. We’re also told that these same isoflavones have a significant anti-cancer effect.
On the plus side, other studies have shown a role for soy in lowering cholesterol and preventing coronary artery disease (which are not the same thing, I may point out). And the anti-meat forces love it. As Sally Fallon and Mary G. Enig, Ph.D., pointed out in a recent article, ‘Soy serves as milk and meat for a new generation of politically correct vegetarians.’ If soy provides protein, fights cancer, eases the symptoms of menopause and lowers the risk of heart disease, what could be wrong?
Well, as with most things in life, it’s just not that simple.
Fallon and Enig, the most vocal and research-savvy of the soy critics, raise a number of troubling points that seem to have been lost in a sea of marketing slogans. They’re worth considering.
- Soy products contain a number of ‘anti-nutrients.’ Chief among them are enzyme inhibitors that block the action of trypsin and other enzymes that you need to digest protein properly. These enzyme inhibitors can cause gastric distress, interfere with protein digestion and, in animal testing, cause pathological conditions of the pancreas. These ‘trypsin inhibitors’ are also growth inhibitors.
- Soy is not a complete protein. It is missing methionine, which is an essential amino acid. If soy is your main source of protein, you will almost certainly not be getting enough vitamin B-12, which is hard enough for adults to absorb in any case, even from animal foods.
- Soy contains phytic acid, which results in the reduced bioavailability of iron and zinc
- Soy contains goiterogenic compounds, which undermine the healthy functioning of the thyroid gland. As Dr. Harold Kristal points out, ‘Sub-clinical hypothroidism is already such a common health problem that caution is certainly warranted.’ In addition, three further points need to be made.
One: Most of the soybeans produced in the U.S. are genetically engineered, the implications of which have not yet been fully understood.
Two: The healthiest soy foods are the fermented ones such as tempeh and miso, which don’t have any of the problems mentioned above but aren’t necessarily the ones we’re eating the most of.
Three: Probably most importantly, the phytoestrogens in soy — those very compounds so touted for their health benefits — are actually a mixed blessing. Yes, they are weaker than ‘real’ estrogen, and yes they bind to the estrogen receptors in your body, which partially prevent the body’s own estrogen from binding to those sites and possibly causing mischief. But they can theoretically help reduce the downside of estrogen (breast cancer, for example). Doesn’t it make sense to consider whether that benefit might be washed away by consuming so much of the phytoestrogens that you might as well be taking the ‘real’ thing?
I posed these questions to Dr. Barry Sears, who just wrote a very good book about incorporating soy into his Zone-type diet (The Soy Zone) when he was on my radio show last week. Going down the list of arguments made by Fallon and Enig, I basically said to him ‘Barry, you got ‘lot of ‘splaining to do!’
While I can’t say he put my mind at ease 100 percent, his answers definitely shed some light on the situation.
For one thing, in the best of all possible worlds, Dr. Sears doesn’t recommend that you get all of your protein from soy. A mix of soy and animal products would be ideal, and with that, I agree completely.
For another, Dr. Sears agrees that while the health benefits of some of these soy compounds are unquestionable, it’s the old American propensity for thinking ‘if some is good, a hundred times that is better’ that is causing a lot of the problem. It’s one thing to get a reasonable dose of isoflavones — such as genistein — from soy. It’s quite another to take isolated supplements of these compounds in amounts several hundred times what is found in the food. In high amounts, isoflavones may have negative effects on other hormones (such as thyroid), and taking hundreds of times the dosage of a weaker estrogen might well be erasing the benefits of phytoestrogens in the first place. Finally, who knows what the cumulative effect of having this much phytoestrogen exposure in our food supply has had on sexual maturity and development in young people?
I agree completely with Dr. Sears that soy can be part of a healthy diet, but for right now, I don’t think we should eat unlimited amounts of it, and I definitely don’t think we should be taking supplements of concentrated isoflavones.
And I am pretty sure that the best soy products continue to be those that are fermented, rather than those that are highly processed.
In a few weeks, when Sally Fallon comes on my show, I may change my mind. But for now, soy products and soy protein gets a qualified thumbs-up from me, especially if used in moderation, not in supplement form, and mostly from fermented products such as tempeh and miso.