I’m a fertility expert – here’s why women don’t need to worry about UPFs

Infertility has been added to the list of health problems claimed to be caused by eating too much processed food, like takeaways, ready meals and pre-prepared snacks.

Men who eat more ultra-processed food (UPFs) take longer to get their partners pregnant, according to a study out this week. And when women do get pregnant, if they have a diet high in UPFs, their embryos develop more slowly.

But other experts have said the research is not convincing evidence that UPFs are really causing fertility problems.  

“These results are not enough to action any change in behaviour in people ,” said Dr Channa Jayasena, a fertility doctor at Imperial College London. “Bombarding people [with diet advice] can make them miserable and stressed, which can aggravate fertility.”

Couples trying to conceive have long been advised to have a good diet and to follow other general health advice like avoiding smoking and drinking. But it’s unclear just how strict they need to be – and healthy eating advice has changed over time.

A recent diet trend is to focus on UPFs, with some campaigners urging people to avoid not just takeaways and snacks, but any kind of premade food, including breakfast cereals, sauces and soups – even supermarket bread. This means all meals and snacks are supposed to be made from scratch.

Stunting, jaw shrinkage, infertility…

Studies have linked UPFs with a range of problems, from clearly diet-related conditions like obesity, to more surprising ones such as mental ill health, stunting in children and even jaw shrinkage (supposedly because processed food tends to be less chewy).

Perhaps it was inevitable then, that UPFs would also be investigated for a role in fertility. In the latest study, the diets were analysed of nearly 1,500 Dutch men and women who were trying to conceive.

Various aspects of their pregnancy were noted, like how long it took to conceive and the health of the baby.

A correlation between high UPF consumption and a slightly lower fertility rate in men and slightly slower growth rate of the embryo initially were the two findings emerged.

“Our findings suggest that a diet low in UPFs would be best for both partners, not only for their own health, but also for their chances of pregnancy and the health of their unborn child,” said Dr Romy Gaillard, a paediatrician at Erasmus University Medical Center in Rotterdam, who led the study.

But, could Gaillard be speaking too soon? This kind of study is not the “gold standard” of medical research, the randomised trial, where some participants take a certain medicine, the rest get placebo tablets, and at the end, their health is compared.

Instead, the Dutch team just observed correlations between what kind of food people ate and their pregnancy outcomes.

The problem is that people who eat more home-cooked meals may be healthier than junk food fans in a range of ways – for instance, they also tend to be wealthier and consume less alcohol and drugs. Such “confounders” could be the real explanation for why UPFs correlates with lower fertility.

The researchers tried to adjust their figures to take account of such potential sources of bias. “But it is very difficult to do that accurately, and because the effects that they observe are so small, those confounders could make all the difference,” said Jayasena.

“If something was having a massive effect, then I would say: ‘That looks pretty obvious’. But actually, it’s so marginal that it wouldn’t surprise me if another study came out and failed to show that.”

‘Barrage’ of health advice

The findings do suggest any effects of UPFs on fertility need more research, he said. But it’s far too soon to change existing health advice. “Couples with fertility problems are faced with a barrage of advice from the media. It’s such a stressful time.”

“I worry that giving them yet another thing that they must do risks them not stopping smoking, for example. The strength of evidence behind traditional lifestyle approaches like exercise and diet is phenomenally strong, and that’s what people really should focus on.”

Some couples who are struggling to get pregnant follow diet advice so strictly it could add to their stress and be counterproductive, he said.

“If you take all the enjoyment out of everything, then it can leave people miserable,” he said. “It is important to reassure couples that in the larger scheme of things, of course it’s good on the whole to be healthy. But you’ve got to live as well.”

Jayasena was not the only expert to doubt that the study was reason for anyone to change their behaviour.

 “There’s too much statistical uncertainty,” said Professor Kevin McConway, a statistician at the Open University.

Professor Gunter Kuhnle, a nutritionist at the University of Reading said: “Making bold claims based on a single observational study is always worrying – especially when the results are likely to cause distress to some people.”

The study was published in the journal, Human Reproduction. Gaillard was approached for comment.