Soy-based foods may lower sperm count: study

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The study is the largest in humans to look at the relationship between semen quality and a plant form of the female sex hormone estrogen known as phytoestrogen, which is plentiful in soy-rich foods.

"What we found was men that consume the highest amounts of soy foods in this study had a lower sperm concentration compared to those who did not consume soy foods," said Dr. Jorge Chavarro of the Harvard School of Public Health in Boston, whose study appears in the journal Human Reproduction.

"It was a relatively large difference," Chavarro said in a telephone interview.

Chavarro said studies in animals have linked high consumption of plant-derived estrogens known as isoflavones with infertility, but so far there has been little evidence of their effect in humans.

"We wanted to know if it would affect sperm production and could serve as a marker for the effects on the reproductive system," Chavarro said.

STRIKING DIFFERENCE

Chavarro's team analyzed the intake of 15 soy-based foods in 99 men who went to a fertility clinic between 2000 and 2006.

They were asked how much and how often in the prior three months they had eaten soy-rich foods including: tofu, tempeh, tofu or soy sausages, bacon, burgers and mince, soy milk, cheese, yogurt and ice cream, and other soy products such drinks, powders and energy bars.

Because different foods have different levels of isoflavones in them, the researchers set a standard for serving sizes of particular foods. Then they divided the men into groups according to soy consumption levels. Men in the highest group on average ate half a serving per day.

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