Lower Sperm Concentrations And Soy Foods Linked

Medical News Online

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
research published online in Europe's leading reproductive medicine
journal, Human Reproduction, today (Thursday 24 July). 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.

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Article adapted by Medical News Today from original press release.
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[1] Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic. Human Reproduction. Published online under advance access. doi:10.1093/humrep/den243.

Source: Emma Mason

European Society for Human Reproduction and Embryology

Main Category: Men's health
Also Included In: Sexual Health / STDs;  Nutrition / Diet
Article Date: 24 Jul 2008 - 5:00 PDT