Hamilton, ON, Mar. 19, 2026 – Women who consume lower amounts of ultra-processed foods have higher odds of conceiving, according to new research from McMaster University. The link persists even after accounting for age, weight, lifestyle and other health factors.
The study analyzed data from over 2,500 women who participated in the National Health and Nutrition Examination Survey (NHANES) – a U.S. survey that combines interviews, 24-hour dietary recalls and laboratory tests to capture detailed information on diet, demographics, health status and biomarkers.
Researchers found distinct differences in eating patterns of women who reported infertility, defined as a lack of conception after one year of trying, and those who did not.
Women reporting infertility consumed more ultra-processed foods, making up about 31 per cent of their daily intake, and scored lower on adherence to the Mediterranean diet, a healthy eating pattern rich in fruits and vegetables, whole grains and healthy fats.
The findings suggest that what we eat – and the degree to which it is processed – may influence reproductive health in a manner well beyond calories or weight.
"Most of what we hear about ultra-processed foods focuses on calories and obesity. But our findings suggest something potentially more complex – there seems to be another mechanism at play which may reflect pathways beyond calories or weight, including chemical exposures that have been hypothesized in prior literature," explains Anthea Christoforou, assistant professor in the Department of Kinesiology and senior author of the paper.
Even if nutrient intake looks fine, eating more ultra-processed foods means more exposure to additives and chemicals that go beyond calories, she adds.
"Ultra-processed foods often carry chemicals like phthalates, BPA and acrylamides, which can leach from packaging or even from the plastic machinery used during processing. These compounds are known to disrupt hormones, and that may be part of why we're seeing a link," says Angelina Baric, a co-author and graduate student in the Department of Kinesiology.
The Mediterranean diet showed a positive association with fertility, but this benefit disappeared once obesity was factored in, suggesting its effect may come from helping maintain a healthy weight and metabolism.
The findings, published today in Nutrition and Health , underscore the need for dietary guidance targeting women of reproductive age. While the effect may look modest on an individual level, in fully adjusted models higher ultra-processed food intake was associated with a roughly 60 per cent lower odds of fertility. Because this was a cross-sectional study, the findings reflect associations rather than cause and effect. Still, associations of this size could have meaningful implications at a population level, given how commonly ultra-processed foods are consumed.
"Very few studies have asked a fundamentally female-specific question: how does what women eat influence their reproductive health? Fertility is a huge outcome, and this is the first time anyone has examined these dietary patterns and infertility at this scale," says Christoforou.
"It suggests diet may be an important and measurable factor associated with women's ability to conceive. It's one thing to say ultra-processed foods contribute to weight gain or cardiometabolic disease. But if they're also affecting hormone pathways, that's a much bigger issue — and it's something people aren't as aware of," she says.
This latest study builds on previous research from the team, which linked ultra-processed foods to poor health outcomes .
"Processing affects foods in ways that aren't reflected in nutrients alone – from chemical exposures during manufacturing to ingredients that displace whole, protective foods," says Baric.
"It's not about perfection – it's about noticing how food is processed, choosing more foods in their natural states and picking ingredients you recognize. Even that simple shift can lower exposure to things we still don't fully understand."
