Years ago, I read a news article about a doctor and his male patient based in Texas which discussed the negative side effects of drinking too much soy milk. The patient developed 'man breasts' and was concerned, and the doctor came to the conclusion the soy caused this.
Are there any scientific studies done in this area that prove or disprove such claims? If so, what are those studies? What's the conclusion?
There are studies. Short answer is: No, soy doesn't give guys boobs.
Paper "Hormonal Effects of Soy in Premenopausal Women and Men" clearly states there is a weak effect upon (cis)women and no adverse effect upon (cis)men.
“Soy and isoflavone consumption does not seem to affect the endometrium in premenopausal women, although there have been weak estrogenic effects reported in the breast. Thus, studies in women have mostly been consistent with beneficial effects, although the magnitude of the effects is quite small and of uncertain significance. Only three intervention studies reported hormonal effects of soy isoflavones in men. These recent studies in men consuming soyfoods or supplements containing 40–70 mg/d of soy isoflavones showed few effects on plasma hormones or semen quality. These data do not support concerns about effects on reproductive hormones and semen quality.”
Accessed from: http://jn.nutrition.org/content/132/3/570S.full
womenis a valid tag if someone wants to ask 'what kind of health issues could women develop by going vegan?' Within a few months someone could ask more questions using these tags and if you delete them now I'm afraid someone is going to re-introduce it eventually. E.g., this post already asks a sub-question involving low iron diet and women. I can see someone breaking it out into it's own separate question.