Ultra-processed foods and fertility: what a new human study suggests before conception

IVF.net Newsdesk

31 March 2026

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A growing body of reproductive research is asking a broader question than whether diet matters in pregnancy. It is asking whether the food choices made by both partners before conception may already be shaping fertility and the earliest stages of embryonic development. A new study in Human Reproduction adds an important piece to that picture by linking higher intake of ultra-processed foods, or UPFs, with lower fertility in men and with subtle differences in early embryonic growth in women.

The study came from the Generation R Study Next Programme in the Netherlands and included 831 women and 651 male partners who were followed from the preconception period or early pregnancy onward. Researchers assessed diet during early pregnancy, at a median of about 12 weeks, using a detailed food-frequency questionnaire. They then classified foods by the degree of processing and expressed UPF intake as a percentage of total food intake by grams per day. Median UPF intake was 22 percent for women and 25 percent for men. Fertility outcomes were assessed through time to pregnancy, fecundability, and subfertility, while embryonic development was measured by transvaginal ultrasound at 7, 9, and 11 weeks of gestation.

What makes this paper especially interesting is that it looks at both sides of the couple at once. Reproductive medicine has often placed the weight of preconception health on women, but this study deliberately examined maternal and paternal diet together. That matters because conception is a shared biological process, and the quality of sperm, the uterine environment, and the metabolic context around implantation all contribute to what happens next.

The central finding was a sex-specific pattern. Higher paternal UPF consumption was associated with reduced fertility, including decreased fecundability and a higher risk of subfertility. In practical terms, couples in which the male partner consumed more UPFs tended to take longer to conceive. By contrast, higher maternal UPF intake was not consistently associated with time to pregnancy, but it was associated with slightly smaller embryonic growth and smaller yolk sac volume, particularly early in the first trimester. The yolk sac is a small but essential structure in early pregnancy, helping support the embryo before the placenta fully takes over.

These developmental differences were small, and the authors are careful not to overstate them. This is an observational study, so it does not prove that UPFs directly caused the fertility changes or the altered growth patterns. But the results are still notable because early embryonic growth has been linked in prior work to later outcomes, including preterm birth and lower birth weight, while abnormal yolk sac development has been associated with miscarriage risk and other complications. Small shifts in early development may therefore matter even when they look modest on the ultrasound screen.

The paper also raises an important mechanistic question. Why might paternal diet show up more clearly in fertility measures, while maternal diet appears more closely tied to early embryonic growth? One likely explanation is timing and route of influence. Sperm may be especially vulnerable to poor diet quality through effects on production, motility, integrity, and oxidative stress. Maternal diet, meanwhile, may act more directly through the environment in which the embryo develops from the very start, including nutrient availability and the biology of the yolk sac. The authors also note that UPFs may not be acting through poor nutrition alone. Additives, packaging-related exposures, and microplastics remain plausible candidates that deserve closer study.

There is another reason this study deserves attention. The Dutch cohort had relatively modest UPF exposure compared with countries such as the United States and the United Kingdom, where UPFs can account for about half of daily intake. Even in this population, the associations were detectable across the full range of intake. That means the findings may have broader implications in settings where processed foods make up a much larger share of the diet.

For IVF professionals and reproductive scientists, the paper is less a call for alarm than a call for precision. It adds to a larger shift in thinking about preconception care. Instead of focusing narrowly on maternal behavior after pregnancy begins, the field is moving toward a couple-based view of reproductive readiness. Diet quality before conception may be one more variable that influences how quickly pregnancy is achieved and how robustly the embryo develops in its earliest days.

It is also a reminder that not all dietary risk is dramatic or obvious. Ultra-processed foods are often not a single category of indulgence but a routine part of modern eating: packaged breads, sweetened drinks, ready meals, processed snacks, and highly formulated convenience foods. Their ubiquity makes them difficult to study cleanly, but also highly relevant. When a signal appears despite that background noise, it is worth taking seriously.

The most responsible interpretation is a measured one. This study does not mean that eating UPFs causes infertility, nor does it define a fertility-safe threshold. But it does strengthen the case for discussing diet as part of preconception counseling for both partners. In reproductive medicine, small influences accumulated across time can become clinically meaningful. The possibility that everyday dietary patterns could shape sperm-related fertility on one side and early embryonic development on the other is exactly the kind of finding that deserves careful follow-up.

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24 March 2026. Focus on Reproduction