A study from Loma Linda University Medical School in southern California found vegetarians and vegans had on average 50 million sperm per ml. Meat eaters had a dramatically higher amount - 70 million sperm per ml.
The research suggests that vegetarians and vegans may be harming their chance of having children in the future. For most meat-eating males, 60% of the sperm they have will be "active." For vegetarians and vegans in the study, this percentage halved.
"We found that diet does significantly affect sperm quality. Vegetarian and vegan diets were associated with much lower sperm counts than omnivorous diets,” Dr Eliza Orzylowska an obstetrician at Loma Linda University Medical Centre told The Telegraph.
“Although these people are not infertile, in is likely to play a factor in conception, particularly for couples who are trying to conceive naturally - the old fashioned way.”
The study authors concluded that vitamin deficiencies from a lack of meat are the most likely causes of a lower sperm count. They also added that, by replacing meat with soy-based products, vegetarians and vegans could be lowering their sperm count further.
Previous research has linked soy to infertility. Researchers from The Harvard School of Public Health said plant oestrogens in foods such as tofu, soy mince or milk may interfere with hormonal signals which can lead to problems with sperm production.
"It’s hard to tell people not to be vegetarians if they are trying to conceive," Dr Orzylowska commented. "But I would caution against using soy, at least for 74 days beforehand, which is the time it takes for sperm to be replaced.”
The latest research will be presented at American Society of Reproductive Medicine’s annual meeting in Hawaii.