Ultra-processed food linked to reduced fertility in men

By Stephen Beech

Men who eat bacon and sausages will find it harder to father a baby, suggests new research.

Eating large amounts of ultra-processed food is linked not only to reduced fertility in men, but also to slower growth of babies in the womb, according to the findings.

Ultra processed foods, or UPFs, are ready-to-eat-or-heat items made with ingredients extracted from foods or synthesised in labs, with little or no whole foods in their composition.

They are often high in added sugar, fat and salt, and low in protein and fibre.

Common examples include bacon and sausages, breakfast cereals, ham, burgers, ice cream, crisps, mass-produced bread, canned baked beans, biscuits, fizzy drinks, fruit-flavoured yoghurts, instant soups, and some alcoholic drinks.

The authors of the new Dutch study, published in the journal Human Reproduction, say their findings suggest that reducing the consumption of UPFs- especially around the time of conception and pregnancy- is better for both parents and their unborn babies.

Although the well-being of both men and women are known to influence reproductive success and the development and health of offspring, no study until now had investigated the combined impact of mothers’ and fathers’ UPF consumption on the length of time it takes to conceive and early embryonic development.

UPF consumption has been rising rapidly with surveys suggesting it accounts for more than half of the food eaten each day in the UK and the United States.

Study leader Dr. Romy Gaillard, Associate Professor of developmental epidemiology at Erasmus University in Rotterdam, The Netherlands, said: “Even though UPFs are so common in our diets, very little is known about their potential relationship with fertility outcomes, and early human development."

Dr Gaillard and colleagues analysed findings from 831 women and 651 male partners enrolled in a study that has been following parents from before conception onwards and into their offspring’s childhood.

Couples were included during the pre-conception period or during pregnancy between 2017 and 2021.

Researchers assessed the parents’ diet with a questionnaire during early pregnancy around 12 weeks.

The different foods were classified as either non-UPFs or UPFs, and UPF intake was expressed as a percentage of total food intake in grams per day.

All the women were pregnant at the time of this questionnaire.

The average consumption of UPFs was 22% and 25%, respectively, of women’s and men’s total food intake.

A questionnaire also provided information on time to pregnancy, fecundability - the probability of conceiving within one month and subfertility - a time to pregnancy of 12 months or more, or the use of assisted reproductive technology.

The distance between the embryo’s head and its buttocks which is an indication of its size and development, and the volume of the yolk sac were measured by ultrasound at seven, nine and 11 weeks of gestation.

Study first author Celine Lin, a doctoral student at Erasmus University, said: “We observed that UPFs consumption in women was not consistently related to the risk of subfertility and time to pregnancy, but was associated with slightly smaller embryonic growth and yolk sac size by the seventh week of pregnancy.

"These differences in early human development were small, but are important from a research perspective and at population level, as we showed for the first time that UPF consumption is not only important for health of the mother, but may also be related to development of the offspring.

“In men, we observed that higher UPF consumption was related to a higher risk of subfertility and a longer duration until pregnancy was achieved, but not with early embryo development.

"This association may be explained by the sensitivity of sperm to dietary composition, whereas maternal UPF consumption may directly influence the environment in the womb in which the embryo develops from the start of life onwards.”

Dr. Gaillard said: “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.”

Other studies have shown that slower embryonic growth in the first trimester is associated with an increased risk of health issues for mother and baby, including premature birth, low birth weight, and an increased risk of heart and blood vessel problems in childhood.

Impaired yolk sac development is associated with an increased risk of miscarriage and premature birth.

Dr. Gaillard said: “Our study shows for the first time that UPF consumption in men and women is associated with fertility outcomes and early human development, but also has limitations.

"Importantly, as this is an observational study, our study shows associations, but cannot prove direct causal effects of UPF consumption on these early life outcomes.

“More research is needed to replicate our findings, in diverse populations, and to study the potential biological mechanisms underlying this effect.

"For instance, are these differences driven by the low nutritional value of UPFs or by the increased exposure to additives or microplastics?

"We also want to study whether these early differences have consequences for birth outcomes, growth and development of offspring throughout childhood."

She added: "Our research shows that we should think more broadly about fertility and early pregnancy.

"We should move away from the idea that only the health and lifestyle of mothers-to-be is important for pregnancy and offspring outcomes, and recognise that the health and lifestyle of both the mother- and father-to-be play an important role.

"Our results highlight the need to pay more attention to male health in the preconception period, which has traditionally been overlooked.”