When couples decide that they are ready to have a baby, the woman’s health usually becomes the focus.
She may start taking prenatal vitamins, reduce alcohol, improve her diet and scrutinize everything from her medications to her skin-care products. Meanwhile, her male partner may receive little more than a reminder to stop smoking and avoid hot tubs.
This imbalance has never made much biological sense. A baby receives half of its genetic material from the egg and half from the sperm. Both are shaped by the health and environment of the person producing them.
New research on ultra-processed foods provides another important reason to pay much more attention to the male partner’s diet before conception.
What are ultra-processed foods?
Almost all food undergoes some processing. Freezing vegetables, pasteurizing milk and grinding oats do not make these foods unhealthy.
Ultra-processed foods are different. They are industrial formulations that often contain refined starches, added sugars, modified oils, flavour enhancers, emulsifiers, colourings, preservatives and other ingredients that would not ordinarily be used in a home kitchen.
Examples may include:
- Sugary drinks and energy drinks
- Packaged pastries, cookies and candy
- Many breakfast cereals and snack bars
- Instant noodles
- Chicken nuggets and other reconstituted meat products
- Some frozen meals
- Packaged chips and snack foods
- Many fast-food products
Not every food that comes in a package is ultra-processed, and one occasional convenience food is unlikely to determine anyone’s fertility. The concern is the overall dietary pattern—particularly when these products displace vegetables, fruit, legumes, whole grains, nuts, seeds, eggs, fish and other minimally processed foods.
What did the new study find?
A 2026 study published in Human Reproduction examined ultra-processed food consumption in 831 women and 651 male partners participating in Generation R Next in the Netherlands.[1]
Generation R is a large research program based at Erasmus University Medical Center in Rotterdam—the “R” refers to Rotterdam. The original Generation R Study began following children from fetal life onward to investigate how genetics, parental health, lifestyle, and environmental exposures influence their growth, development, and long-term health.
Generation R Next begins even earlier. It follows prospective parents from around the time of conception, through pregnancy and into their children’s lives. Researchers collect information about the health and lifestyle of both partners, time to pregnancy, fertility treatment, pregnancy outcomes, and embryonic and fetal development.[1]
This makes it particularly valuable for studying how the health of both future parents may influence fertility and the earliest stages of life.
In this study, ultra-processed foods accounted for a median of approximately 22% of the women’s total food intake and 25% of the men’s total food intake, measured by weight in grams per day.[1]
These estimates are worth noting because they were considerably lower than those reported in some other high-income countries, where ultra-processed foods may make up approximately half or more of the average diet.[1] If an association can be detected in a population with relatively moderate consumption, the question becomes even more relevant in countries where ultra-processed foods make up a much larger proportion of daily food intake.
Higher consumption of ultra-processed foods by men was associated with a longer time to pregnancy and a greater likelihood of subfertility. In other words, the clearest association with the couple’s ability to conceive was found in the male partner’s diet.[1]
The women’s consumption of ultra-processed foods was not consistently associated with the time it took to conceive. However, higher maternal consumption was associated with slightly smaller embryonic growth measurements and yolk-sac size early in pregnancy.[1]
These embryonic differences were small, and we do not yet know whether they translate into meaningful differences in pregnancy or childhood outcomes. Nevertheless, the findings raise an intriguing possibility: the father’s diet may have a particularly important relationship with the couple’s ability to conceive, while the mother’s diet may also influence the environment in which the embryo begins to develop.
The study was observational, so it cannot prove that ultra-processed foods caused these differences. Couples who consume more ultra-processed food may differ in other ways that are difficult to measure completely.
Another important limitation was that all women included in the dietary analysis were already pregnant when they completed the food questionnaire, at approximately 12 weeks. The study reported time to pregnancy retrospectively and did not include couples who never conceived. The findings should therefore be interpreted as an important signal rather than proof of cause and effect.[1]
A controlled trial strengthens the concern
A 2025 controlled crossover nutrition trial published in Cell Metabolism supports the findings.[2]
In that study, men consumed both an ultra-processed diet and an unprocessed diet under controlled conditions. The researchers also compared diets providing appropriate and excess amounts of calories. This helped them investigate whether the effects were related to food processing itself rather than simply to higher calorie intake.[2]
The ultra-processed diet adversely affected several metabolic and reproductive measures. Reported changes included alterations in reproductive hormones and sperm function, as well as weight, body fat, and cholesterol-related measures. Some adverse effects were found even when total calories were controlled.[2]
The researchers also found higher blood concentrations of one phthalate metabolite during the ultra-processed-food phase. This does not prove that phthalates caused the reproductive changes, but it raises questions about exposures introduced through food production, processing, or packaging.[2]
This was a relatively small, short-term study, and it measured reproductive biomarkers rather than pregnancy or live-birth rates. We cannot conclude that a few weeks of eating ultra-processed food will make a man infertile.
However, the findings suggest that the association between ultra-processed foods and male reproductive health may not be explained by calories or body weight alone.
Something about the overall dietary pattern—and possibly the processing itself—may matter.
Why might the male diet have such an important effect?
Sperm are constantly being produced. Their development takes about two and a half to three months, during which nutrition, metabolic health, inflammation, oxidative stress, heat, smoking, alcohol, environmental exposures, and other lifestyle factors may influence them.
A diet dominated by ultra-processed foods may affect sperm through several overlapping pathways.
Nutrient displacement
When packaged snacks, sugary drinks and ready-to-eat products make up much of the diet, they often replace foods that provide folate, zinc, selenium, omega-3 fats, antioxidants, fiber and other nutrients involved in reproductive health.
Metabolic dysfunction
Ultra-processed dietary patterns may promote insulin resistance, visceral fat accumulation, and changes in metabolic hormones. These changes may affect testosterone production and the hormonal signals involved in spermatogenesis.
Inflammation and oxidative stress
Sperm cell membranes are particularly vulnerable to oxidative damage. Excessive oxidative stress may affect sperm concentration, motility and DNA integrity.
Additives and packaging exposures
Ultra-processed foods may increase exposure to substances introduced during manufacturing, processing or packaging. Researchers are investigating whether food additives, endocrine-disrupting chemicals or microplastics could contribute to reproductive effects, but the evidence is not yet sufficient to identify a single culprit.
The effect is unlikely to come from one ingredient alone. It may result from a combination of lower nutritional quality, metabolic consequences, and exposures associated with industrial processing.
Fertility preparation must include the man
For too long, preconception advice has placed most of the responsibility on women.
Women are often expected to change their diet, monitor their cycles, take supplements, attend appointments and carry the emotional burden of trying to conceive. Yet male factors contribute to a substantial proportion of fertility difficulties, either alone or in combination with female factors.
The emerging research on ultra-processed foods does not prove that a man’s diet is always more important than a woman’s. However, it demonstrates that the male diet may be at least as important as the female diet—and potentially more important for some aspects of fertility than we have traditionally recognized.
In the Generation R Next study, the clearer association with time to pregnancy and subfertility was found in men, not women.[1] That is an important finding.
We should stop treating the male partner as a supporting character in fertility preparation. His health, nutrition, and exposures form an essential part of the reproductive environment.
What should couples do?
The goal does not need to be a perfect, completely unprocessed diet. That would be unrealistic for most people and could create unnecessary anxiety around food.
Instead, both partners can begin by shifting the balance:
- Replace sugary drinks with water, sparkling water or unsweetened tea.
- Choose fruit, nuts, plain yogurt or vegetables more often than packaged snack foods.
- Build meals around recognizable ingredients rather than industrial formulations.
- Prepare larger portions of simple meals and freeze the extras.
- Read ingredient lists, not only calorie counts.
- Include the male partner in nutrition and preconception appointments.
- Begin making changes at least three months before trying to conceive whenever possible.
It is also important not to equate “healthy” with expensive, exotic or complicated. Oats, lentils, beans, frozen vegetables, eggs, canned fish, brown rice, fruit and nuts can all form part of a practical preconception diet.
The bigger message
The most important lesson from this research is not that one food causes infertility. Fertility is far more complex than that.
The lesson is that preconception health belongs to both partners.
The months before pregnancy are a biologically important window when eggs, sperm, hormones, and metabolic health are all influenced. We should use that window to support the health of the future mother, the future father, and the embryo they hope to create.
Women have carried most of the responsibility for reproductive preparation for far too long. It is time to bring men fully into the conversation—not only because it is fair, but because the science increasingly suggests that it matters.
Dr Marina OBGYN
References
- Lin, Celine, et al. “Periconceptional Ultra-Processed Food Consumption in Women and Men, Fertility, and Early Embryonic Development.” Human Reproduction, 2026. https://doi.org/10.1093/humrep/deag023.
- Preston, Jessica M., et al. “Effect of Ultra-Processed Food Consumption on Male Reproductive and Metabolic Health.” Cell Metabolism 37, no. 10 (2025): 1950–1960.e2. https://doi.org/10.1016/j.cmet.2025.08.004.
