Men’s Junk Food Habits Can Wreck Their Fertility, Study Warns

When couples struggle to conceive, the focus typically lands on the woman. Her diet, her age, her stress levels get scrutinized from every angle. But a new study out of the Netherlands suggests it might be time to pay a lot more attention to what the man is eating. Specifically, how much ultra-processed food he consumes may be linked to lower chances of conceiving.

Researchers followed hundreds of couples from before or during early pregnancy and found that men who ate more ultra-processed food, including packaged snacks, sugary drinks, processed meats, and industrially manufactured convenience items, were more likely to experience fertility difficulties. For every standard increase in a man’s ultra-processed food intake, the odds of subfertility jumped by 36 percent, even after accounting for other lifestyle factors like smoking, drinking, age, and their partner’s own diet.

The study also uncovered a separate but equally concerning pattern in women: mothers who consumed more of these heavily processed foods were linked to slightly smaller embryos early in pregnancy, along with reduced development of the yolk sac, a temporary organ that nourishes the embryo before the placenta takes over. These effects were most visible at seven weeks of pregnancy and faded somewhat as the first trimester progressed.

How Men’s Junk Food Habits Were Measured

Published in Human Reproduction, the research was part of the Generation R Next Study, a large ongoing project based in Rotterdam that tracks couples from before conception through their children’s early years. The team included 831 women and 651 of their male partners, all of whom filled out detailed food questionnaires during early pregnancy, at a median of about 12 weeks along.

Each participant reported what they ate over the previous four weeks, covering more than 200 food items. Researchers then sorted every item using a well-known classification system that groups foods based on how much industrial processing they’ve undergone. The most heavily processed category includes products typically loaded with added sugars, unhealthy fats, salt, and chemical additives while being low in fiber and nutrients. After sorting, the team calculated what percentage of each person’s total daily food intake came from ultra-processed sources.

The median ultra-processed food intake was 22 percent of total food consumed for women and 25.1 percent for men. Those figures are actually below the national average in the Netherlands and well below rates in some countries where ultra-processed foods account for up to 50 to 60 percent of daily calories.

To measure fertility, researchers collected data on how long each couple tried before conceiving. Subfertility was defined as taking 12 months or longer to get pregnant, or needing assisted reproductive technology such as IVF. About 30.6 percent of the women in the study met that threshold. For embryonic development, trained technicians performed detailed ultrasound exams at roughly 7, 9, and 11 weeks of pregnancy, measuring the length of the embryo and the volume of the yolk sac.

Ultra-Processed Food and Fertility: What the Study Found

Results divided sharply depending on whether researchers looked at the mother or the father.

For men, the link between processed food and fertility trouble was consistent. Higher ultra-processed food consumption was associated with a lower probability of conceiving in any given month. Men in the highest quarter of ultra-processed food intake had 69 percent higher odds of being classified as subfertile compared to men in the lowest quarter. These associations held up even after the researchers adjusted for a long list of possible confounding factors, including the female partner’s own ultra-processed food consumption.

For women, ultra-processed food intake showed no consistent link to how long it took to conceive. But it did appear to matter for what happened after conception. At seven weeks of pregnancy, higher maternal ultra-processed food consumption was associated with smaller embryo size, specifically a reduction of 0.13 standard deviations in embryo length per standard unit increase in processed food intake. There was also a parallel reduction in yolk sac volume at the same stage: a decrease of 0.14 standard deviations per unit increase in intake. Women in the highest quarter of ultra-processed food consumption had yolk sac volumes that were 0.41 standard deviations smaller than those in the lowest quarter at seven weeks.

These early differences appeared to soften by nine and eleven weeks, which could point to a kind of catch-up growth, though the study didn’t test that directly. It may also suggest that the influence of diet is strongest during the very earliest and most vulnerable stages of development. Researchers noted that impaired growth during the first trimester has been linked in prior studies to complications like preterm birth, low birth weight, and even unfavorable heart health later in childhood.

The father’s diet did not appear to meaningfully affect embryonic growth or yolk sac development. The study authors suggested this may indicate that the mother’s direct biological connection to the developing embryo, through nutrient supply in the womb, has a more immediate impact during those early weeks than any indirect effects from the father’s sperm quality.

Why Ultra-Processed Food May Be the Culprit

The study didn’t test exactly why this happens, but the researchers offered a few likely explanations.

For men, adequate nutrition is needed for healthy sperm production and function. Diets heavy in processed foods tend to lack the vitamins, minerals, and healthy fats that sperm cells need to develop properly and move effectively. Poor diet may also increase oxidative stress, a buildup of harmful molecules that can damage cells, which could impair the tiny energy-producing structures within sperm that keep them functional.

There’s also the packaging to consider. Ultra-processed foods frequently come wrapped in materials containing chemicals that can interfere with the body’s hormone systems. These substances have been linked in other research to altered hormone levels that may affect reproductive function.

For women, the mechanism may be more direct: eating more processed food likely means consuming fewer of the nutrients that a rapidly developing embryo needs. The yolk sac, which acts as the embryo’s main nutrient pipeline before the placenta is ready, may be particularly sensitive to what nutrients are or aren’t available. If the yolk sac can’t do its job properly, embryonic growth could suffer as a result.

Worth noting is that these patterns emerged in a relatively healthy population. Participants were largely well-educated, and their ultra-processed food consumption was below national averages. If measurable effects on fertility and embryonic development show up at these moderate intake levels, the consequences for populations with much higher processed food consumption could be serious.

This study is the first to examine the combined impact of both partners’ ultra-processed food intake on fertility and early pregnancy development in a general population. The distinct, sex-specific patterns it uncovered, with processed food linked to men’s ability to conceive and women’s early embryonic development, reinforce something fertility experts have been saying with increasing urgency: preconception health is not just a woman’s concern. What a man puts on his plate before his partner gets pregnant may play a bigger role than often assumed.

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Disclaimer: This article is based on findings from a single observational study and does not establish direct cause and effect. Results may not apply to all populations. This content is intended for informational purposes only and should not be taken as medical advice. Anyone with concerns about fertility or reproductive health should consult a qualified healthcare provider.

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