Those Interfering Little Soybeans

Halved Sperm Counts

A study published in the journal of Human Reproduction, found that a diet containing even modest amounts of soy may reduce sperm concentrations by half. Authors of the study said the culprit may be phytoestrogens, plant compounds that mimic female hormones and that can be found in such soy-containing foods as tofu, texturized vegetable protein, and soy milk. These plant compounds may interfere with a man's hormonal signals, though one UK expert stressed the fact that Asian men eat lots of soy-based products with no apparent effects on their fertility.

Animal studies conducted in the past have suggested a similar finding of a link between soy and infertility, but past human studies looking at soy consumption have been contradictory.

In this particular study, conducted by the Harvard School of Public Health, 99 men who had attended a fertility clinic with their partners and who had provided semen samples were divided into four groups depending on the amount of soy in their diets. In this case, a significant decrease in sperm counts was found in the semen of the men who ate more soy. Normal sperm counts are considered to be between 80-120 million sperm per milliliter. Men who ate a portion of soy-based foods every other day had 41 million fewer sperm per milliliter.

The leader of this study, Dr. Jorge Chavarro, said that isoflavones, a chemical found in soy, may be the culprit affecting sperm production. Isoflavones have similar effects to human estrogen.

Why Not Asians?

Chavarro noted that overweight men were more prone to the effects of soy on their sperm counts, reflecting the fact that high levels of body fat may lead to increased estrogen production in males. The published results of this study also pointed out the curious fact that Asian men who consume high amounts of soy have found no similar resultant impact on their fertility.

A senior lecturer in andrology from the University of Sheffield, Dr. Allan Pacey, expressed the fact that were soy to have a definite detrimental effect on sperm counts, this would be reflected in Asian countries where soy is a major part of the diet and that there is no evidence that this is the case. Pacey understands that men may be concerned about a possible dietary or lifestyle component to their infertility and comments that, "Estrogenic compounds in food or the environment have been of concern for a number of years, but we have mostly thought that it was boys exposed in the uterus before birth who were most at risk. We will have to look at adult diet more closely, although the fact that such large parts of the world have soy food as a major part of their diet and don't appear to suffer any greater infertility rates than those on western diets suggests that any effect is quite small."