Take report on soy and sperm count study with pinch of salt

The following a letter by Boon Yee Yeong (Ms), a Nutritionist, to the Forum of the Straits Times dated 13 August 2008.

I REFER to the Reuters report 'Soy-based foods linked to low sperm count' (in the Straits Times of July 30 2008). The story, which refers to a study, is misleading.

Based on scientific reviews, this study is confounded by many issues, hence the results should be viewed with much caution.

In the study quoted by the report, Dr Jorge Chavarro found that 'soyfood and soy isoflavone intakes were unrelated to total sperm count, ejaculate volume, sperm motility, or sperm morphology', which are the important measures of sperm quality and male fertility.'
The study also did not determine what other foods, medications, supplements, existing medical conditions, sexual activities or environmental factors may have directly affected the drop in sperm count.

The study also classified high intakes of soyfoods as less than three ounces (85g) of a beverage per day. This is not considered a high intake of any food under most circumstances.

Like most epidemiological reports, this study is retrospective and inherently subject to a variety of biases. The total study population was small, 100 subjects, and little is known or reported about other dietary, stress factors, medications, or lifestyle issues that might also affect sperm count in these men.

It is well-established that of all semen parameters, variation in count is highly variable from day to day and seasonally in all men.

Dr Chavarro found that the men with the highest soyfood intake produced more ejaculate fluid volume with equivalent amounts of sperm count as those with lower intakes. This 'watering-down effect' of sperm concentration should not be mistakenly associated with a decrease in fertility.

Obesity may be the explanation for the negative findings of this study. Dr Chavarro found high soyfood intakes were associated with lower sperm concentration, but 'the association was more pronounced among overweight and obese men than among lean men.'

Men with high levels of body fat are likely to produce more oestrogen than their slimmer counterparts.

Dr Chavarro's study conflicts with the large body of research including United States government and National Institute of Health-sponsored human and primate research, in which controlled amounts of isoflavones from soy were fed and no effect on quantity, quality or motility of sperm were observed.

Boon Yee Yeong (Ms)
Nutritionist
Director, Food & Nutrition Specialists
Singapore