There has been some concern that consumption of phytoestrogens might exert adverse effects on men's fertility, such as lowered testosterone levels and semen quality. The studies in women have provided modest support for beneficial effects. One cross-sectional study showed serum estrogens to be inversely associated with soy intake.
Seven soy intervention studies controlled for phase of menstrual cycle. Soybeans are rich in a special class of polyphenol known as isoflavones or phytoestrogens as they are found to mimic the female hormone estrogen. They believe soy isoflavone may reduce the level of testosterone thus lowering sexual function in men.
However, research suggests that soy isoflavones and estrogen have very different mechanisms of action and scanty evidence is available to connect disrupted male fertility with isoflavone intake, most of which are scientifically flawed too. A small, pilot cross-sectional study found that men who were consuming very high amounts of soy foods had lower sperm concentration.
The findings associated lower sperm concentration with higher ejaculation volume in men due to high consumption of soy foods. The same research group produced similar data in that failed to produce an association between soy food intake among men and fertility. On the contrary, well-designed clinical interventions revealed no association between isoflavone intake and sperm concentration or quality.
A study reported no effect on semen quality in healthy men who consumed a supplement containing 40 mg of isoflavones daily for two months. A clinical intervention resonated with this outcome. Two case reports, one involving a 60 year old man and the other involving a year-old type 1 diabetes male reported feminising effects, believed to occur due to soy food consumption.
In a review , the author reported neither isoflavone supplements nor isoflavone-rich soy foods affected total or free testosterone levels, sperm quality and oestrogen circulation. Another large meta-analysis published in Fertility and Sterility analysed 15 placebo-controlled studies with and 32 reports involving 36 treatment groups found neither soy foods nor isoflavone supplements had any effect on bioavailable testosterone concentrations in men of all ages.
Considering this evidence, the two case reports mentioned at the beginning of this section, therefore, suggest over-consumption-related abnormality that can be observed for any food, not only soy. Prostate cancer is a huge concern among older males. Phytoestrogens are plant components found in several different types of food but the amounts in soy are much greater than other foods.
However, despite being classified as plant estrogens, soybean isoflavones differ at both the molecular and clinical levels from the human hormone estrogen. The origin of the concern about hormone disruption has a lot to do with two case reports each describing individual men who experience hormonal disturbances that allegedly occurred as a result of consuming soy foods.
But — and this is important to note — each of the men described in these reports consumed extremely high amounts of soy foods, about nine times the amount of isoflavones typically consumed by older men in Japan, a country for which soy is a traditional component of the diet. Too much of any food may lead to health problems. Furthermore, the soy intake of these two men occurred in the context of nutrient-deficient diets since most of their calories were derived from one food.
In contrast to these two case reports, extensive clinical data show that neither soy foods nor isoflavones affect testosterone and estrogen levels in men. This is true even when intake greatly exceeds typical Japanese intake.
Generally, more refined soy products such as isolated soy protein have much lower isoflavone concentrations. However, the very opposite might be true: research indicates soy may reduce the risk of prostate cancer in men. This is important information since prostate cancer is the second most commonly occurring cancer in men worldwide. In a recent review of 30 observational studies , high soy consumption was linked to a significantly lower risk of developing the disease.
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