Here are studies regarding the affect on testosterone, which relates well to my admittedly blaze comment about fried testicals, by which I meant that the male sex hormone system is overwhelmed by phytoestrogens:
1995
Keung WM. Dietary estrogenic isoflavones are potent inhibitors of B-hydroxysteroid dehydrogenase of P testosteronii. Biochem Biophys Res Commun 1995 Oct 24; 215(3):1137-1144. The isoflavones diadzein, genistein, biochanin A and formononetin were found to inhibit enzymes that produce steroid hormones critical to reproductive and neurological function, particularly hormones that produce testosterone.
2000
Nagata C and others. Inverse association of soy product intake with serum androgen and estrogen concentrations in Japanese men. Nutr Cancer 2000;36(1):14-8. Researchers found lower testosterone levels and higher estrogen levels in Japanese men who consumed higher levels of soy foods.
2000
Habito RC and others. Effects of replacing meat with soyabean in the diet on sex hormone concentrations in healthy adult males. Br J Nutr 2000 Oct;84(4):557-63. Men consuming tofu instead of meat for 4 weeks had lower testosterone-oestradiol ratios as well as changes in other hormone levels. “Thus, replacement of meat protein with soyabean protein, as tofu, may have a minor effect on biologically-active sex hormones which could influence prostate cancer risk.”
2003
Wisniewski AB and others. Exposure to genistein during gestation and lactation demasculinizes the reproductive system in rats. Journal of Urology, April 2003 169:1582-1586. In order to determine the effects of exposure to phytoestrogens, researchers at the Johns Hopkins Children’s Center and the Johns Hopkins Bloomberg School of Public Health randomly assigned pregnant female rats to diets containing none, low and high levels of genistein–the major type of phytoestrogen in soy. The male offspring were thus exposed to genistein indirectly through maternal consumption during pregnancy and lactation. Female rats on the low-genistein diet received between 0.1 and 1.0 mg genistein per day while those on the high-genistein diet received between 6.4 and 23.6 mg genistein per day–somewhat equivalent to the exposure of mothers consuming small amounts and large amounts of soy. Male offspring of mothers on the high-genistein diet exhibited reproductive abnormalities and rats exposed to both the low- and high-genistein diets had shorter testes length, larger prostate mass and lower testosterone concentrations. The researchers also looked at adult sexual behavior of male offspring. Those exposed to both low and high doses of genistein were less likely to ejaculate after mounting female rats. Most interesting was the fact that males exposed to the low dose were less likely to mount and begin the process of intercourse than males whose mothers received the free or high-genistein diets. Thus, although adult sperm counts were not affected by exposure to genistein, the male rats exhibited “persistent demasculinization of the male reproductive system.” Ejaculatory behavior was significantly reduced by exposure to genistein. Most significant was the observation that “the low dose led to alterations in male development to a greater degree than the high dose.” This is consistent with other studies reporting “an inverted U-shaped dose response” in males exposed to low and high doses of estrogenic substances. What this means is that pregnant and nursing mothers should avoid all soy as even a low-dose exposure to genistein caused subtle but significant changes in sexual behavior in male offspring.
2003
Gardner-Thorpe D and others. Dietary supplements of soya flour lower serum testosterone concentrations and improve markers of oxidative stess in men. Eur J Clin Nutr 2003 Jan;57(1):100-6. In a study carried out at University Hospital of Wales, male volunteers ate three scones per day in addition to their normal diet for a period of six weeks. The scones were made either with wheat flour or soy flour providing 120 mg per day of isoflavones (about the amount contained in 3 cups of soy milk). Researchers noted “significant improvements in two of the three markers of oxidative stress” and concluded that "these findings provide a putative mechanism by which soya supplements could protect against prostatic disease and atherosclerosis. However, testosterone levels fell in the volunteers eating the soy but researchers did not stress this alarming finding in their conclusion.
2007
Goodin S and others. Clinical and biological activity of soy protein powder supplementation in healthy male volunteers. Cancer Epidemiol Biomarkers Prev 2007;16:829–33. Twelve men 18 years or older were fed 56 grams of pure soy per day for 28 days. Over the 28 days the men experienced a 19% drop in serum testosterone.