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In this post, Nutrition Diva's answer for question #10 "Any good suggestions for getting enough protein as a vegetarian?" includes soy. While the rest of her answers appear to be on track with the latest studies (vs. what a lot of doctors/"experts" recommend), this one in particular worries me. (I blame @codinghorror for tweeting this post in the first place :))

From what I've read, phytoestrogens (which non-fermented soy is extremely high in) have been shown to contribute to many problems for males, specifically with cancer and fertility issues. I believe there are also cancer-related issues for females but haven't read as much on the subject. Unfortunately, neither books (e.g. Slow Death by Rubber Duck), nor video (e.g. The Disappearing Male) are easily linkable and I hesitate to take random sources procured from searches since they don't tend to be based on actual peer-reviewed, unbiased (i.e. non-sponsored) studies.

Is there a (linkable) affirmative source that has the same information?

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Question about nutrition are off topic according to the new FAQ. –  Baarn Oct 5 '12 at 22:32

3 Answers 3

Can't speak for every nutritionist, but I endorse soy (in moderation and minimally processed) as a protein source because:

  • It's protein rich (33% of cals from protein)
  • Contains all the essential amino acids (i.e., is a "complete" protein)
  • Is inexpensive, versatile, and appropriate for vegans.

Large, independent studies show that moderate amounts of soy protein have beneficial effects on heart disease risk factors and may even help protect against prostate cancer. However, I do recommend limiting it to 2-3 servings a day, which--based on the evidence I've reviewed--poses no danger to endocrine balance or function.

Here are some citations that might help reassure you:

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Great answer @Monica, good to see something nutrition related being backed up so strongly :-) –  Ivo Flipse Nov 12 '11 at 8:32
    
This would be a more accurate post if you reworded the claims. The papers you listed find evidence that reduced disease risk is CORRELATED with soy consumption, not (as you imply) CAUSED by it. –  J. Winchester Jun 22 '12 at 0:19

I thought that this article (with more pubmed links) had an interesting perspective as well. The primary point is that the current science is inconclusive, but that the large quantities of phyto-oestrogens during infancy is probably a bad idea.

This overview of high-soy-intake cases highlights the problems with phytoestrogens as well:

One study reported that a 19-year-old male developed decreased libido, erectile dysfunction, and low testosterone after consuming very large quantities of soy as part of a vegan diet. The researchers did not, however, report the presence of gynecomastia (a.k.a male breasts). It should also be noted that the patient had type 1 diabetes, indicating some level of metabolic dysfunction, and relied on soy as his primary protein source. The symptoms disappeared one year after discontinuing his vegan diet.

Another study reported that one 60-year-old man developed breasts, as well as sexual dysfunction, after consuming three quarts of soy milk daily for six months. Again, the symptoms faded after discontinuation of the soy intake.

Extreme case studies aside, soy intake appears to be safe at normal to moderately high levels, even those above the relatively high consumption level of Asian men. Problems only seem to arise when soy is consumed at levels 9 – 10 times the norm for several months at a time.

Extremely high intake seems to be problematic, but as the article notes, "it’s the dose that makes the poison."

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...science or art :P Sorry this was partially a joke and reality, it is extremely hard to do unbiased reasearch on this area. It is big a decision making problem in itself to process the scientific material -- you get many pareto-optimal points in your multivariate MILP -problem if you are really trying to quantify this objectively... and in every step, you can do mistakes... –  user2598 Dec 28 '11 at 4:42

Inertia, it takes a while for information to propogate. Also, soy is attached to ideology. It's the answer, particularly for vegans, on how they can get protein without animal products (while conveniently ignoring/never knowing in the first place that to grow plants you need nitrogen in the fertilizer, and guess where the nitrogen comes from?). Try to tell them soy is harmful and they'll ignore you the same way they ignore you if you tell them that some people lack the enzymes to get protein from plant sources. Try to tell a vegetarian that they shouldn't eat soy and they'll get very upset at you, because that means no tofu dogs, tofurkey, tofu burgers, tofu chicken, and every other fake meat that's made from heavily processed soy. It's more religion than science for a lot of them.

As long as vegans see soy as the magical bean, soy will keep getting recommended in the face of any research that shows it to be bad for you.

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-1 You say it is more religion than science for them but you don't care to back up your claims either. "there is no conclusive […] evidence of harm" (source). –  Baarn Dec 23 '12 at 10:58

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