Men who eat soy-based foods may be harming their fertility, doctors say after a study found a link between soy-rich diets and lower sperm counts.
The study showed men who ate more than two portions of soy-based foods a week had, on average, 41 million fewer sperm per ml of semen than men who had never eaten soy products.
The apparent fall in sperm count is unlikely to make healthy men infertile, but some experts say it could have a significant impact on those who already have a lower than average sperm count.
A sperm count of between 80 million and 120 million per ml is regarded as normal, while men who produce fewer than 20 million sperm per ml are regarded as clinically sub-fertile.
The study, by Jorge Chavarro at Harvard School of Public Health in Boston builds on previous research in animals and on human tissues that have suggested certain ingredients in soy can harm sperm production.
Male fertility has been in decline in the West for several decades, with about 20 percent of young Europeans having a low sperm count, while levels of soy have risen steadily in the Western diet since the 1940s because it is a cheap source of protein.
Soy-based products are now found in two-thirds of manufactured food, including sweets, pasta, bread, and cookies and crackers, according to the Institute of Food Research in Norwich, England.
In the biggest human study into the effects of soy on fertility, Chavarro and colleagues at Massachusetts General Hospital recruited 99 men who had visited a fertility clinic between 2000 and 2006.
The men were asked to fill out a questionnaire regarding the amounts of 15 different soy foods they had eaten over the previous three months. The researchers then put the men into four groups according to the levels of chemicals called isoflavones in their diets.
Isoflavones are ingredients in soy products that mimic the female sex hormone, estrogen. Each man then provided a sperm sample for testing.
Chavarro found that men who consumed at least half a portion of soy food a day had the lowest sperm counts.
"Our findings suggest that the greater the soy food intake is, the lower the sperm concentration, compared with men who never consume soy food," said Chavarro, whose study appears in the journal of Human Reproduction.
Hi Sunnygirl, You have to wait for the starter's pistol.
Science seems to be a tough study for some people, coldly joining the dots never seems to yield the emotional highs that some people yearn. If a study doesn't look right it is hard to have much confidence in it, the countries that eat the most soy foods are also the most populous countries, wouldn't that alone start alarm bells ringing in clever students?
Not everyone is convinced that Jorge Chavarro is even close to right, but he did get a book or three out of it.
Read my links, I have the courage to display them.
No link between sperm and soy. Healthy weight important for male fertility
Recent claims of a link between the consumption of soy foods and sperm concentration are incorrect according to a leading Australian dietitian who has reiterated the importance of soy foods in the diet of Australian men.
A small study by Dr Jorge Chavarro, published in the Journal of Human Reproduction found that a group of men consuming half a portion of soy food a day experienced reduced sperm concentration.
However, Dr Chavarro admitted that the lower sperm concentration could be put down to the fact that 72% of the men in the trial were overweight or obese. Men with high levels of fat produce more oestrogen than their slimmer counterparts.
With less than 100 subjects, the study was also very small and did not acknowledge the large normal variation in sperm counts, which can fluctuate widely from day to day and seasonally in all men.
Accredited Practising Dietitian Michelle McCracken from the Sanitarium Nutrition Service said the trial did not find a direct connection between soy intake in men and reduced fertility.
"This study found no relationship between soy foods and total sperm count and a range of other important measures of sperm quality and male fertility. It also failed to determine how factors such as other foods, medications, environmental influences or existing medical conditions may have affected a drop in sperm concentration," she said.
"Dr Chavarro found that men with the highest soy intake produced more ejaculate fluid volume with equivalent sperm count as those with lower intakes, and this larger volume lead to the lower sperm concentrations in higher intake individuals. This watering-down effect of sperm concentration should not be mistakenly associated with a decrease in fertility."
Ms McCracken said this type of observational study is unreliable in pinpointing a cause of any results and that the findings should be considered with caution.
"This is the first study to find a correlation between soy intake and reduced sperm concentration. Other research on soy in men has not found a negative impact on male hormones, but rather has suggested a preventive effect in prostate cancer," she said.
"Asian populations have long consumed diets with much higher concentrations of soy foods than those consumed by the men in the study without signs of reduced fertility," said Ms McCracken.
Ms McCracken said that if any conclusion can be drawn, it is the importance of men maintaining a healthy weight, and that soy foods are an important part of a balanced diet.
"Sanitarium recommends men continue to follow the Australian Dietary Guidelines that promote a diet based on a wide variety of foods, including plenty of fruits, vegetables and legumes such as soybeans and other soy foods," she said.
Maybe you should read Chavarro's comments again, after the abstract.....
The study appears in the journal of Human Reproduction. Here’s the abstract via PubMed:
BACKGROUND: High isoflavone intake has been related to decreased fertility in animal studies, but data in humans are scarce. Thus, we examined the association of soy foods and isoflavones intake with semen quality parameters.
METHODS: The intake of 15 soy-based foods in the previous 3 months was assessed for 99 male partners of subfertile couples who presented for semen analyses to the Massachusetts General Hospital Fertility Center. Linear and quantile regression were used to determine the association of soy foods and isoflavones intake with semen quality parameters while adjusting for personal characteristics.
RESULTS: There was an inverse association between soy food intake and sperm concentration that remained significant after accounting for age, abstinence time, body mass index, caffeine and alcohol intake and smoking. In the multivariate-adjusted analyses, men in the highest category of soy food intake had 41 million sperm/ml less than men who did not consume soy foods (95% confidence interval = -74, -8; P, trend = 0.02). Results for individual soy isoflavones were similar to the results for soy foods and were strongest for glycitein, but did not reach statistical significance. The inverse relation between soy food intake and sperm concentration was more pronounced in the high end of the distribution (90th and 75th percentile) and among overweight or obese men. Soy food and soy isoflavone intake were unrelated to sperm motility, sperm morphology or ejaculate volume.
CONCLUSIONS: These data suggest that higher intake of soy foods and soy isoflavones is associated with lower sperm concentration.
Relax, don’t freak out just yet. “It's way too early to say stop eating soy foods. It's not time to worry about whether you're eating too much soy. There's not enough information to conclusively say that,” lead researcher Dr. Jorge Chavarro, M.D., a research fellow at the Harvard School of Public Health, told Steven Reinberg of HealthDay News.
Cheers
Science seems to be a tough study for some people, coldly joining the dots never seems to yield the emotional highs that some people yearn. If a study doesn't look right it is hard to have much confidence in it, the countries that eat the most soy foods are also the most populous countries, wouldn't that alone start alarm bells ringing in clever students?
Not everyone is convinced that Jorge Chavarro is even close to right, but he did get a book or three out of it.
Read my links, I have the courage to display them.
No link between sperm and soy. Healthy weight important for male fertility
Recent claims of a link between the consumption of soy foods and sperm concentration are incorrect according to a leading Australian dietitian who has reiterated the importance of soy foods in the diet of Australian men.
A small study by Dr Jorge Chavarro, published in the Journal of Human Reproduction found that a group of men consuming half a portion of soy food a day experienced reduced sperm concentration.
However, Dr Chavarro admitted that the lower sperm concentration could be put down to the fact that 72% of the men in the trial were overweight or obese. Men with high levels of fat produce more oestrogen than their slimmer counterparts.
With less than 100 subjects, the study was also very small and did not acknowledge the large normal variation in sperm counts, which can fluctuate widely from day to day and seasonally in all men.
Accredited Practising Dietitian Michelle McCracken from the Sanitarium Nutrition Service said the trial did not find a direct connection between soy intake in men and reduced fertility.
"This study found no relationship between soy foods and total sperm count and a range of other important measures of sperm quality and male fertility. It also failed to determine how factors such as other foods, medications, environmental influences or existing medical conditions may have affected a drop in sperm concentration," she said.
"Dr Chavarro found that men with the highest soy intake produced more ejaculate fluid volume with equivalent sperm count as those with lower intakes, and this larger volume lead to the lower sperm concentrations in higher intake individuals. This watering-down effect of sperm concentration should not be mistakenly associated with a decrease in fertility."
Ms McCracken said this type of observational study is unreliable in pinpointing a cause of any results and that the findings should be considered with caution.
"This is the first study to find a correlation between soy intake and reduced sperm concentration. Other research on soy in men has not found a negative impact on male hormones, but rather has suggested a preventive effect in prostate cancer," she said.
"Asian populations have long consumed diets with much higher concentrations of soy foods than those consumed by the men in the study without signs of reduced fertility," said Ms McCracken.
Ms McCracken said that if any conclusion can be drawn, it is the importance of men maintaining a healthy weight, and that soy foods are an important part of a balanced diet.
"Sanitarium recommends men continue to follow the Australian Dietary Guidelines that promote a diet based on a wide variety of foods, including plenty of fruits, vegetables and legumes such as soybeans and other soy foods," she said.
Maybe you should read Chavarro's comments again, after the abstract.....
The study appears in the journal of Human Reproduction. Here’s the abstract via PubMed:
BACKGROUND: High isoflavone intake has been related to decreased fertility in animal studies, but data in humans are scarce. Thus, we examined the association of soy foods and isoflavones intake with semen quality parameters.
METHODS: The intake of 15 soy-based foods in the previous 3 months was assessed for 99 male partners of subfertile couples who presented for semen analyses to the Massachusetts General Hospital Fertility Center. Linear and quantile regression were used to determine the association of soy foods and isoflavones intake with semen quality parameters while adjusting for personal characteristics.
RESULTS: There was an inverse association between soy food intake and sperm concentration that remained significant after accounting for age, abstinence time, body mass index, caffeine and alcohol intake and smoking. In the multivariate-adjusted analyses, men in the highest category of soy food intake had 41 million sperm/ml less than men who did not consume soy foods (95% confidence interval = -74, -8; P, trend = 0.02). Results for individual soy isoflavones were similar to the results for soy foods and were strongest for glycitein, but did not reach statistical significance. The inverse relation between soy food intake and sperm concentration was more pronounced in the high end of the distribution (90th and 75th percentile) and among overweight or obese men. Soy food and soy isoflavone intake were unrelated to sperm motility, sperm morphology or ejaculate volume.
CONCLUSIONS: These data suggest that higher intake of soy foods and soy isoflavones is associated with lower sperm concentration.
Relax, don’t freak out just yet. “It's way too early to say stop eating soy foods. It's not time to worry about whether you're eating too much soy. There's not enough information to conclusively say that,” lead researcher Dr. Jorge Chavarro, M.D., a research fellow at the Harvard School of Public Health, told Steven Reinberg of HealthDay News.
Cheers
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