I dont like Soy, never have, probably never will after these findings...
Some argue its fine, others do not. Its not part of my diet, so I guess that explains my standpoint on it.
Soy Foods Are Associated With Lower Sperm Concentrations
ScienceDaily (July 24, 2008) — Men who eat an average of half a serving of soy food a day have lower concentrations of sperm than men who do not eat soy foods, according to new research. The association was particularly marked in men who were overweight or obese, the study found.
In the largest study in humans to examine the relationship between semen quality and phytoestrogens (plant compounds that can behave like the hormone, oestrogen), Dr Jorge Chavarro, a research fellow in the department of nutrition at Harvard School of Public Health, Boston, USA, and his colleagues found that men who ate the most soy food had 41 million sperm per millilitre less than men who did not consume soy products. (The "normal" sperm concentration for men ranges between 80-120 million/ml).
Isoflavones (daidzein, genistein and glycitein) are plant-derived compounds with oestrogenic effects that are found mainly in soy beans and soy-derived products. Animal studies have linked the high consumption of isoflavones with infertility in animals, but so far there has been little evidence of their effect in humans.
Dr Chavarro and his colleagues analysed the intake of 15 soy-based foods in 99 men who had attended a fertility clinic with their partners to be evaluated for sub-fertility between 2000 and 2006. They asked them how often and how much they had eaten in the previous three months; the foods included tofu, tempeh, tofu or soy sausages, bacon, burgers and mince, soy milk, cheese, yoghurt and ice cream, and other soy products such as roasted nuts, drinks, powders and energy bars.
Different foods have different levels of isoflavones in them, and so the researchers related the size of the serving to the particular food. For instance, a standard serving of tofu was 115g and for soy milk it was one cup (240 millilitres).
The men were divided into four groups according to their intake of soy foods and isoflavones. After adjusting for factors such as age, abstinence time, body mass index (BMI), alcohol and caffeine intake and smoking, Dr Chavarro found that men in the highest intake category had, on average, 41 million sperm/ml less than men who did not eat soy foods. "Men in the highest intake group had a mean soy food intake of half a serving per day: in terms of their isoflavone content that is comparable to having one cup of soy milk or one serving of tofu, tempeh or soy burgers every other day," he said.
"It is important to highlight that the figure of half a serving a day is the average intake for men in the highest intake group. Some men in this group had intakes of soy foods as high as nearly four servings per day."
The researchers found evidence that the association between soy food intake and sperm concentrations were stronger in men who were overweight or obese (and 72% of them were). They also found the relationship between soy foods and sperm concentration was strongest in men with the higher sperm concentrations. "The implication is that men who have normal or high sperm counts may be more susceptible to soy foods than men with low sperm counts, but this remains to be evaluated," explained Dr Chavarro.
The study does not reveal why soy foods have this effect on sperm, but Dr Chavarro speculates that increased oestrogenic activity may have an adverse effect on the production of sperm by interfering with other hormonal signals. This effect could be strengthened further in overweight and obese men because men with high levels of body fat produce more oestrogen than slimmer men, leading to high overall levels of oestrogen in the body and reproductive organs.
Soy foods are the most important source of phytoestrogens in people in the Western world, and the researchers say they were able to comprehensively assess the men's soy intake. They did not assess intake of isoflavones from other sources, such as bakery products made with soy flour. "However, the most likely effect of not assessing intake of these foods is that the associations reported in this study are attenuated," said Dr Chavarro.
The researchers say that the clinical significance of their research remains to be determined, and further randomised trials are needed.
This is the real killer for me.
Clinical and biological activity of soy protein powder supplementation in healthy male volunteers.
Goodin S, Shen F, Shih WJ, Dave N, Kane MP, Medina P, Lambert GH, Aisner J, Gallo M, DiPaola RS.
Department of Medicine, University of Medicine and Dentistry of New Jersey/Robert Wood Johnson Medical School, New Brunswick, NJ 08***-2681, USA. [email protected]
PURPOSE: To determine if a commonly used soy protein supplement exhibits biological activity in vivo and in vitro, we evaluated an over-the-counter soy protein powder supplement using blood from healthy male volunteers and in an estrogen receptor in vitro assay. SUBJECTS AND METHODS: We recruited healthy male volunteers 18 years of age or older that were in good health. Treatment consisted of consuming two scoops (56 g) of pure soy protein powder (Puritan's Pride, Oakdale, NY) daily for 28 days. Serum testosterone and luteinizing hormone (LH) levels were collected on days -7, 0, 14, and 28 of therapy, and day 42. A reporter estrogen receptor (ER) assay was used to determine the effect on ER-beta and ER-alpha in vitro. RESULTS: Twelve subjects were enrolled with a mean age of 32.25 years (range 25 to 47). Serum testosterone decreased 19%(+/-22%) during the 4-week use of soy protein powder (P = 0.021) and increased within 2 weeks after we discontinued soy protein powder. Serum LH concentrations decreased during the 4-week use of soy protein powder then increased within 2 weeks after we stopped the soy protein powder, but the changes did not reach statistical significance (P = 0.20). Soy protein powder was found to induce agonist activity to ER-beta using a reporter estrogen receptor assay in yeast. CONCLUSION: Soy protein powder decreases serum testosterone levels in healthy men and acts as an ER-beta agonist; the significance of this biological effect with respect to cancer prevention needs further study.
But there is some good from this study...
Another note to take from this study is this, "...and acts as an ER-beta agonist..". This tells us its good at fighting gyno. ER-beta inhibits proliferation and increases differentiation in cells, which is a good thing for those wanting to reverse gyno or have symtpoms. So its not all bad.