Ultra-Processed Food and Fertility: What the Studies Actually Show

"Ultra-processed food" has become one of the most-used phrases in nutrition, and fertility headlines have followed. Some of those headlines are fair. Others turn a three-week trial in 43 young men into "junk food makes you infertile." Because you're the one deciding what goes in your cart, it's worth knowing what each study actually did.

Contents

• What counts as ultra-processed
• The controlled trial in men
• Semen quality studies
• The 2026 couples study
• All the evidence in one table
• Why processing might matter
• What to do with this

What counts as ultra-processed

Most research uses the NOVA system, which sorts foods by the nature, extent and purpose of the industrial processing they go through, from unprocessed foods like fresh vegetables, eggs and plain meat to "ultra-processed" industrial formulations. In everyday terms, the ultra-processed group includes most soft drinks, packaged snacks and sweets, many ready meals, and products with long ingredient lists of things you wouldn't cook with at home.

In January 2026 the 2025–2030 Dietary Guidelines for Americans made the first explicit federal recommendation to limit highly processed, packaged or ready-to-eat foods, sugar-sweetened beverages, refined carbohydrates and products with chemical additives. So this isn't a fringe idea anymore. The fertility-specific question is narrower: does the processing itself affect reproduction, and how strong is the evidence?

The controlled trial in men

The most rigorous study so far was published in Cell Metabolism in 2025 by researchers at the University of Copenhagen and partners. It's worth understanding its design, because it answers a question observational studies can't.

• Who: 43 healthy men aged 20 to 35.
• Design: A crossover trial. Each man ate both an ultra-processed diet and an unprocessed diet for three weeks each, separated by a three-month washout. The diets were matched for calories, protein, carbohydrate and fat, and participants weren't told which diet they were on.
• Calorie twist: Half the men ate a calorie-matched diet and half ate about 500 extra calories a day, so the researchers could separate the effect of processing from the effect of simply eating more.

On the ultra-processed diet, regardless of calories, the men gained weight (about 1 kg more fat mass, per the university's summary) and had a worse LDL-to-HDL cholesterol ratio. Levels of follicle-stimulating hormone (FSH), which drives sperm production, went down. Sperm quality showed a trend toward impairment, with lower total motility, but that change wasn't statistically significant. Blood levels of a phthalate metabolite called cxMINP also trended upward. Phthalates are plastic-associated chemicals that can disrupt hormones.

This trial builds on a well-known 2019 NIH study by Kevin Hall's team, in which 20 adults living in the NIH Clinical Center ate about 500 more calories a day and gained about 0.9 kg in two weeks on an ultra-processed diet, compared with a minimally processed diet offering the same nutrients. That study showed ultra-processed food tends to drive overeating. The Copenhagen trial suggests some effects show up even when overeating is controlled.

Semen quality studies

A 2024 study in Nutrients looked at 126 healthy young men in Italy, average age 20. Their diets were classified using NOVA. Compared with men eating the least ultra-processed food, those in the highest quarter had lower sperm concentration and lower progressive motility, and normal-shaped sperm tended to decrease as intake rose.

This is a cross-sectional study: one snapshot in time. It can't show that the food caused the differences, and men who eat more ultra-processed food may differ in sleep, activity, weight, smoking or alcohol. But it lines up with the direction of the controlled trial, which is why researchers are taking it seriously. For a fuller picture of what drives semen quality, see our male fertility diet plan and howtohaveababy.com's list of ways to improve sperm health.

The 2026 couples study

The newest and in some ways most relevant study was published in Human Reproduction in March 2026. Researchers in Rotterdam followed 831 women and 651 male partners in the Generation R Next cohort, enrolled before conception or in early pregnancy. They estimated each partner's ultra-processed food intake as a share of total food (median about 22% for women and 25% for men) and compared it with time to pregnancy and early embryo growth on ultrasound.

• Men: Higher ultra-processed food intake was associated with a higher risk of subfertility and a longer time to pregnancy.
• Women: Intake was "not consistently related" to subfertility or time to pregnancy.
• Embryo growth: Higher intake in women was associated with slightly smaller embryos and yolk sacs by week 7. The researchers described the differences as small. The male partner's intake wasn't linked to embryo growth.

The authors were clear that an observational study "cannot prove direct causal effects," and that results need replicating. They also noted that Dutch diets contain less ultra-processed food than typical U.S. or U.K. diets, which may limit how far the numbers generalize. Their conclusion was still practical: a diet low in ultra-processed food would be best for both partners.

All the evidence in one table

Why processing might matter

Researchers are weighing several explanations, and they aren't mutually exclusive:

• Overeating and weight gain. The 2019 NIH study showed ultra-processed diets lead people to eat more, and the men in the 2025 trial gained fat on the ultra-processed diet within weeks.
• Diet quality. Ultra-processed foods tend to crowd out vegetables, legumes, nuts, fish and whole grains.
• Additives and packaging chemicals. The Copenhagen trial's rise in a phthalate metabolite raises the possibility that chemicals from processing or packaging play a role. The Rotterdam team also raised additives and microplastics as open questions.
• Something about processing itself. Because the 2025 trial matched calories and nutrients, its authors argued that the processed nature of the food was the issue. Exactly what that means biologically is still unknown.

What to do with this

Nobody needs to eat a "clean" diet to conceive, and food stress isn't good for anyone. A more useful goal is to change the default for the meals you eat most often. A few swaps that make a real difference without taking over your life:

1. Drinks first. Sugar-sweetened beverages are one of the easiest ultra-processed categories to replace. Our guide to non-alcoholic beer and mocktails while TTC covers better options if you're also cutting alcohol.
2. Swap the snack, not the meal. A handful of unsalted nuts in place of a packaged snack is the swap with the best fertility trial evidence behind it; see walnuts, nuts and sperm quality.
3. Batch-cook one base. A pot of beans, lentil soup or chili on Sunday replaces several ready meals during the week.
4. Use canned and frozen whole foods. Plain frozen vegetables, canned beans and canned fish are processed in the everyday sense, but they generally aren't considered ultra-processed. Our winter fertility grocery list is built around them.
5. Watch the "healthy" ultra-processed foods. Protein bars, shakes and flavored "fertility" powders often fall into the ultra-processed category. Our protein powder guide covers what to look for if you use them.
6. Make it a couples project. The reproductive evidence so far points mainly at men. If the male partner eats most of his meals on the go, his plate may be the bigger opportunity.

Give changes about three months before expecting any difference in a semen analysis, since that's roughly how long sperm take to develop. And keep perspective: in all of these studies, ultra-processed food was one factor among many. If you've been trying for 12 months (or 6 months if the female partner is 35 or older), a medical evaluation for both partners matters more than any diet change.

Sources

• Preston JM, Iversen J, Hufnagel A, et al. Effect of ultra-processed food consumption on male reproductive and metabolic health. Cell Metabolism. 2025;37(10):1950–1960.e2. Abstract; University of Copenhagen summary: ku.dk
• Donato F, Lorenzetti S, Ceretti E, et al. Consumption of ultra-processed foods and semen quality in healthy young men living in Italy. Nutrients. 2024;16(23). PMID 39683523. Summary
• Lin C, et al. Periconceptional ultra-processed food consumption in women and men, fertility, and early embryonic development. Human Reproduction. 2026. ESHRE press release: focusonreproduction.eu
• NIH. NIH study finds heavily processed foods cause overeating and weight gain (May 16, 2019). nih.gov
• FAO Global Forum on Food Security and Nutrition. Ultra-processed foods, diet quality, and health using the NOVA classification system. fao.org
• AJMC. New HHS dietary guidelines take hard line on processed foods for first time (January 14, 2026). ajmc.com
• ASRM Practice Committee. Definition of infertility: a committee opinion (2023). asrm.org (PDF)