Scientists have warned that poor diets may be behind declining fertility rates in the west, with excessive fat to blame for lowering sperm counts.
Although it is well known that overweight or obese people find it harder to get pregnant than slimmer people, new research suggests that even those who manage to remain slim despite consuming high levels of junk food, are damaging their fertility.
Three new studies presented at a fertility conference in the US suggest that consuming large levels of fat lowers the chance of couples getting pregnant, damages ovaries and produces poor quality embryos.
A team from the Harvard School of Public Health and Massachusetts General Hospital, examined the impact on fertility rates of high trans fat intake in 141 men trying to conceive through IVF. They found that fertilisation rates were lowest in couples where men had diets highest in trans fats, which are found in margarine, cakes, biscuits and takeaway food.
Men with the best diets had 83 per cent chance of getting their partner pregnant, compared with 47 per cent for those with the worst diets, where 20 per cent of calorie intake came from trans fats. And there was a gradual decline in fertility which correlated with an increasingly bad diet, suggesting that the food itself may be causing the problem.
In a separate study, researchers at the University of Colorado, Denver, found that mice fed a high fat diet had damaged ovaries and poor fertility rates, even if they were not overweight.
Researchers believe high fat diets trigger a state of low grade chronic inflammation in the body which damages fertility, perhaps because the body believes it is under stress and so a bad environment for growing a baby.
A third study by the universities of North and South Carolina found that women with low levels of viable embryos and who struggled to get pregnant often had high levels of elaidic acid in their blood streams, suggesting they had eaten a lot of fried food.
Dr Richard Kennedy, the former president of the British Fertility Society, said: “Obesity is a major public health issue and there is no doubt it is related to certain aspects of fertility, specifically egg production and quality.
“Our advice to anyone presenting for IVF, is that if they are over our weight threshold, they should make efforts to reduce their weight.”
Dr Edgar Mocenu, a consultant obstetrician at the Rotunda Hospital Dublin, said that poor diets could be behind fertility decline in the past few decades.
“It’s a general public health issues,” he said, “In recent years men’s sperm counts have dropped from 20 million to 15 million and diet is no doubt a contributory factor.
“This shows that you shouldn’t only focus on a woman’s weight. Often if you see a couple trying to conceive doctors spend a disproportionate amount of time talking to the woman about her weight when they should be also discussing it with the man.”
Fertility expert Professor Charles Kingsland, clinical director of Britain’s largest fertility clinic in Liverpool, said diet was crucial for pregnancy.
“It’s well known that a good balanced diet is good for fertility and unhealthy foods can be harmful particularly if your fertility is poor to start with,” he said.
The research was presented at the annual meeting of the American Society for Reproductive Medicine (ASRM) in Baltimore.
“These kind of studies allow us to better counsel our patients on their nutritional needs while attempting to become pregnant.” said Dr Owen Davis, the president of the ASRM.