Soy Foods Are Associated With Lower Sperm Concentrations

ScienceDaily (July 24, 2008) — 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 new research. 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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I would prefer tomato (lycopene) for lowering testosterone levels to
prevent BPH.  It's not goitrogen and oestrogen either, just lowers T.

Taka