I am hoping that you can comment on the risks and benefits of eating soy protein. In particular, what are you thoughts on the research relating soy consumption with hormonal changes in men and their offspring? Is there any literature on how much is too much? Have you heard of any difficulties experienced by women with soy? I am asking because I have noticed that fitness magazines that cater to both men and women have recently been espousing the benefits of soy, but recall that in the last year or so the pendulum seem to have swung temporarily in the other direction, and wanted to know if there is an evidence based reason for a swing back…
My own personal feeling is that soy protein is unlikely to mess with your hormones whether you’re male or female, at any normal consumption level. Over the years, soy foods have been purported to tame menopausal symptoms, cut heart disease and cancer risks, improve bone density, and many other things. At the same time, many people have wondered if soy can cause undesirable effects in men or breast cancer survivors. The evidence however, hasn’t really panned out consistently for any of these pseudo-medicinal effects, good or bad. It seems that soy is…just a food.
But you’re right, media and magazines seem to change every year on their opinion of soy foods. In 2008 a soy-phobia emerged among men after headlines broadcast a small study that found that obese men who consumed the most soy foods had reduced sperm counts. However, obese men are known to have higher estrogen levels than lean guys (because fat cells produce estrogen), and this effect hasn’t been replicated or supported in other studies.
The most recent meta analysis on the “Men and Soy” topic found no cause for concern. (Hamilton-Reeves JM, Vazquez G, Duval SJ, Phipps WR, Kurzer MS, Messina MJ. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil Steril. June 11, 2009.)
Many of the health effects of eating soy are attributed to compounds known as isoflavones. These are called phytoestrogens, because they can mimic some of the activities of the female hormone, estrogen. But isoflavones are much weaker than estrogen, and the quantities present in soy foods don’t seem to be enough to cause much effect. Many studies on isoflavones use doses from 60-250 mg per day for a period of months, but the average Westerner consumes only about 2 mg a day of isoflavones. (A cup of soymilk has about 30 mg, a serving of tofu about 20 mg. Soy burgers and sausage contain <5 mg isoflavones each)
It’s a pattern with the poor soybean: One study finds reduced cholesterol with soy! And others don’t. One study finds that soy improves bone mass! And others don’t. One study finds soy will reduce testosterone levels! And others don’t. In science, we want to put our faith in health effects that are supported by repeated studies, and in my opinion there isn’t enough evidence that normal intake of soy foods (1-2 per day) will do much of anything to your health beyond it’s normal nutritive value.
That said, while soy may not be impressive as medicine- it’s certainly a good food. As a protein source, soy can be a valuable addition to the diet. Soybeans contain omega 3 fatty acids and fiber, and soy foods offer complete protein with zero cholesterol and less saturated fat than many animal proteins. Replacing high fat meats with soy substitutes is definitely something I would recommend, because it reduces unhealthy dietary components. Keep in mind that increasing meat intake (red particularly) is conclusively linked with increasing cancer and CVD risk. Soy burgers instead hamburgers would surely be a positive change, at least some of the time. For vegetarians, soy foods can provide valuable protein and vitamins, plus increased dietary variety. Soy milk and soy cheese can also be great for people with allergies or intolerances to dairy foods.
The only case in which I would avoid soy is if I were a woman with a past history of estrogen-receptor positive breast cancer. While the jury is still out on this one, I feel that the outcome is sufficiently serious to warrant being extra-conservative.
For everyone else, male or female, I see no reason to curb your intake if you like tofu, soymilk, or edamame. But if you don’t currently eat soy foods, I also wouldn’t worry excessively that you’re missing out on nature’s miracle food.
People tell me all the time they don’t eat soy. While I disagree with their “it’ll give me man-boobs” reasoning, it is not going to hurt anyone to avoid soy, so why argue? I take the same route with people who avoid artificial sweeteners out of fears that they cause cancer – I don’t agree with you, but you have the right to avoid anything that gives you the willies! It certainly won’t hurt you to go through life without Diet Coke. I invite everyone to make their own choice on soy. I choose a lot of soy foods, about 2 a day (mostly dairy replacements) and personally have no worries about my husband consuming them every now and then. If he was consuming 10 servings a day maybe I’d encourage moderation, but I don’t know any guys who eat that much soy. As with most things, moderate intake is no cause for worry.
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