Soy foods shooting down the little guys

We’ve been programmed to believe soy is a health food, but as far sperm are concerned, the lady of the soy bean is a heart breaker.

The vixen in the soy bean

Among the goodies packaged into the tiny yellow bean, which has become a staple of the modern diet, are a group of compounds collectively known as the isoflavones.

The family of plant-derived compounds includes daidzein, genistein and glycitein. They sound pretty healthy and are considered to be flavanoids, which exhibit anti-oxidant properties, but they also show structural similarities to the female hormone, estrogen. The chemical similarity means they can bind to human estrogen receptors and illicit oestrogenic effects.

Animal studies have linked high consumption of isoflavones with infertility in animals. Researchers from Harvard School of Public Health think these plant estrogens, known as phytoestrogens are knocking out human sperm too.

Counting the sperm and soy

The team counted things up in 99 men attending a fertility clinic.

The first thing they counted was the consumption of soy based foods. They identified 15 foods which contain soy and asked the men to indicate how often and how much of the food items, had been consumed in the previous 3 month period.

Foods making the list included tofu, tempeh, 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.

Next they counted the sperm.

Sperm out for the count

The men were divided up into four groups based on their reported soy intake, in addition to their dietary habits, a number of other habits were considered in the final analysis. These habits include how often they were doing it, how often they were drowning their sorrows with alcohol, as well as their caffeine and nicotine habits. Age and body mass index (BMI) also weighed in to the mix.

The study found the big soy eaters weren’t quite shooting blanks, but their sperm count was pretty low – coming in at around 41 million sperm per millilitre. “Normal” studs produce between 80 – 120 million/ml.

For the record, big soy eaters weren’t eating tofu for breakfast, lunch and supper – they averaged half a serving of soy a day. This translates to a glass of soy milk, a protein bar or a tofu hamburger, three or four times a week.

Fatties more sensitive

Men carrying a few extra pounds, seemed particularly vulnerable to be out for the count on a soy diet.

Biologically speaking, this makes a lot of sense. The soy foods are delivering a “healthy” dose of phytoestrogen and fat guys already have a little extra circulating estrogen, because estrogen is among the chemicals fat cells are spewing out on a routine basis.

Estrogen is a girl hormone, so too much of it is not going to make it easy to get the sperm factory firing on all cylinders.

Soy foods not so manly

At the end of the day, eating too much soy might be putting the little guys in jeopardy.

If you’re trying to get pregnant – might be time to ditch the soy sausages and satisfy that man sized hunger with a piece of real meat.

Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic. Human Reproduction (2008) 23(11) 2584-2590. Jorge E. Chavarro , Thomas L. Toth , Sonita M. Sadio , and Russ Hauser.

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