The effect of phytoestrogens on men has been a topic of some debate in recent years. Many believe soy products to be a healthy source of protein for both sexes, while others think phytoestrogens can harm the health of men. A recent study has shown that men eating large amounts of soy, which contain phytoestrogens, have lower sperm counts.
Phytoestrogens are present in plants, and behave in much the same way as the female hormone estrogen. More specifically, phytoestrogens contain isoflavone compounds that are responsible for the estrogen like effects. Soy products, such as soy beans (most popular as the Japanese snack food edamame), soy milk, and other derived forms (soy burgers, tofu, soy ice cream, etc…), contain significant amounts of these isoflavones.
Past research has shown that in animals, high isoflavone consumption can lead to infertility in males. This connection was speculated by some to occur in human males as well, but no significant evidence supported this opinion until this recent study.
A normal sperm count for a healthy male is between 80-120 million/ml. According to the study, individuals who consumed the largest amounts of soy had a drastic 30-50% decrease in sperm count of 41 million/ml. This decrease was also noted to be most pronounced in obese individuals.
The study accounted for 99 men who had attended fertility clinics between 2000 and 2006. The patients were questioned regarding the intake of 15 soy based products, which 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.” Each soy product contains different amounts of isoflavones, so “servings” were standardized for isoflavone content. For example, 115 grams of tofu was considered equivalent to 240 milliliters based on isoflavone content.
The 99 men were separated into four groups ranging from low soy intake to high. High soy intake was considered to be half a serving per day, which is equivalent to one cup of soy milk or half a soy burger. This group had individuals who consumed as much as four servings per day. The highest group, as mentioned above, demonstrated a decrease in sperm count of 41 million/ml compared to men who did not eat soy foods.
Past research has also shown that obesity in men leads to higher production in the body of estrogen, which subsequently is thought to reduce sperm counts (due to speculated interference with other hormones associated with fertility, such as testosterone–this is also the proposed explanation of why phytoestrogens reduce sperm count). It came as no surprise that obese individuals who consumed high levels of soy had the lowest sperm counts of all the patients.
Understanding comprehensively the benefits and risks of soy consumption is a goal for the future, but evidence is mounting that high levels can have negative effects on fertility. The Japanese however, who eat soy beans in place of snacks like chips and peanuts and consume more soy than anyone, have the longest life expectancies of any country in the world. The likelihood is that a balance needs to be found in order to reap soy’s benefits, while not suffering from the potential negative effects.
Source: Defeat Diabetes Foundation: Mason, Emma. Human Reproduction press release. July 2008.