WASHINGTON (AFP) - - Eating or drinking a lot of products containing soy and isoflavones can result in reduced sperm count among men, a Harvard School of Public Health study has shown.

"There has been a lot of interest on whether soy affects fertility because many studies in animals suggest that this is the case, but there are very few studies in humans," said researcher and lead study author Jorge Chavarro.

"This only the third study to look at whether soy food has a relationship with fertility in humans and the first one to find an association in agreement to the animal studies," he told AFP.

Soy contains isoflavones, an organic compound which acts like female hormones and appears to impede a man's ability to produce sperm.

"Isoflavones are structurally similar to estrogen and can mimic the action of estrogen in the body," said Chavarro.

"Soy is expected to have estrogen-like activity in many organs and tissues which can be beneficial for some things but it's certainly not beneficial for sperm production, at least that's what animal models suggest."

The Harvard study examined the soy intake of 99 men, determined to be part of couples experiencing fertility difficulties, over the course of three months.

"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," the study said.

Those who ate the most soy had 41 million sperm per milliliter less than men who did not eat soy. An average man has between 80 million and 120 million sperm per milliliter.