Researchers studied over 800 pregnant women and their partners to see if eating ultra-processed foods (like packaged snacks, fast food, and sugary drinks) before and during early pregnancy affected fertility and baby development. They found that mothers who ate more junk food had babies with slightly smaller measurements in the first weeks of pregnancy, while fathers who ate more junk food took longer to conceive. The study suggests that what both parents eat before getting pregnant might matter more than we thought for having a healthy baby.
The Quick Take
- What they studied: Whether eating ultra-processed foods (junk food) before and early in pregnancy affects how easily couples get pregnant and how well babies develop in the first few weeks
- Who participated: 831 pregnant women and 651 of their male partners from a large health study in the Netherlands. Most were relatively healthy and well-educated, tracked from before pregnancy through childhood
- Key finding: Mothers eating more junk food had babies that measured slightly smaller at 7 weeks of pregnancy. Fathers eating more junk food were about 10% less likely to get their partner pregnant within a month and had higher rates of taking longer than a year to conceive
- What it means for you: If you’re planning to get pregnant or your partner is, eating less junk food might help with fertility and early baby development. However, this study was done in a relatively healthy population, so results may not apply to everyone
The Research Details
This was a cohort study, which means researchers followed a group of people over time and tracked what they ate and what happened to them. The study included 831 women and 651 men from the Generation R Study in the Netherlands, which has been following families since before pregnancy. Researchers asked participants about their diet using a food questionnaire when women were about 12 weeks pregnant. They measured how much ultra-processed food each person ate as a percentage of their total food intake. Ultra-processed foods include things like packaged snacks, fast food, sugary drinks, and processed meats. The researchers also measured babies using ultrasound at 7, 9, and 11 weeks of pregnancy to see how big the embryo and yolk sac (a structure that feeds the early baby) were. They asked couples how long it took them to get pregnant and whether they needed fertility treatments.
This study design is important because it followed people from before pregnancy onwards, which is the best way to see if diet affects fertility and early development. By measuring both parents’ diets and tracking actual pregnancy outcomes and baby measurements, the researchers could see real-world effects rather than just guessing. The study also looked at both mothers and fathers separately, which is important because previous research hadn’t really examined how fathers’ diet affects these outcomes
This study has several strengths: it’s a large, well-designed study that followed people over time, it measured actual baby development with ultrasound rather than just asking people to remember, and it adjusted for many other factors that could affect results (like exercise, smoking, and education). However, the study population was relatively healthy and well-educated, mostly from the Netherlands, so results might not apply to all groups. The study also measured diet only once, so we don’t know if people’s eating habits changed over time
What the Results Show
Mothers who ate more ultra-processed foods had babies with slightly smaller measurements at 7 weeks of pregnancy. Specifically, for every increase in junk food eating, the embryo measured about 0.13 standard deviations smaller (think of this like a small but measurable difference). The yolk sac, which feeds the early baby, was also about 0.14 standard deviations smaller. These differences were most noticeable at 7 weeks and became smaller by 9 and 11 weeks of pregnancy, suggesting the babies caught up in growth.
Fathers who ate more ultra-processed foods had more trouble getting their partners pregnant. Men with higher junk food intake were about 10% less likely to achieve pregnancy within one month. They also had a 36% higher risk of subfertility, meaning it took them a year or longer to conceive or they needed fertility treatments. Interestingly, fathers’ junk food intake didn’t seem to affect how the baby developed in the first trimester—only whether they could get pregnant in the first place.
The median amount of ultra-processed food eaten was about 22% of total food intake for women and 25% for men. This means that on average, about one-quarter of what men ate was ultra-processed food, which is fairly typical in modern diets.
The study found that mothers’ junk food intake did not affect how easily they got pregnant—only fathers’ intake affected fertility. This suggests that men’s diet may be particularly important for sperm health and fertility. The researchers also found that the effects on baby size were temporary, with differences disappearing by later in pregnancy, suggesting babies may catch up in growth
This is one of the first studies to look at how both parents’ junk food intake affects fertility and early baby development together. Previous research has shown that diet affects fertility and pregnancy outcomes, but most studies focused only on mothers. This study adds important information by showing that fathers’ diet matters too, particularly for getting pregnant in the first place. The findings fit with other research showing that ultra-processed foods are linked to worse health outcomes
The study only measured diet once, so we don’t know if people ate the same way throughout the periconception period. The population studied was relatively healthy and well-educated in the Netherlands, so results might not apply to other groups with different diets or health conditions. The study couldn’t prove that junk food caused these problems—only that they were associated. Other unmeasured factors could have played a role. The differences in baby size, while measurable, were small and babies seemed to catch up by later pregnancy
The Bottom Line
If you’re planning to get pregnant or your partner is, reducing ultra-processed food intake may help with fertility and early baby development. This is a moderate-strength recommendation based on this study, though more research is needed. Focus on eating more whole foods like fruits, vegetables, whole grains, and lean proteins, and less packaged and fast foods. This advice applies to both women and men planning pregnancy
Anyone planning to get pregnant in the next year should pay attention to this research, especially men since the fertility effects were stronger in fathers. Women who are already pregnant or trying to conceive should also consider improving their diet. People with existing fertility problems might particularly benefit from dietary changes. However, if you’re not planning pregnancy soon, this research is less immediately relevant to you, though eating less junk food is generally healthy advice for everyone
If you change your diet now, you might see effects on fertility within a few months, since sperm takes about 3 months to develop. For women, dietary changes before pregnancy could affect early baby development, so ideally start eating better a few months before trying to conceive. The effects on baby size appeared early (7 weeks) but were small and temporary
Want to Apply This Research?
- Track the percentage of your daily food intake that comes from ultra-processed foods. Aim to reduce this from the average of 22-25% down to under 15%. Log packaged snacks, fast food, sugary drinks, and processed meats separately to see where most ultra-processed foods are coming from
- Replace one ultra-processed food item per day with a whole food alternative. For example: swap a packaged snack for fruit, fast food lunch for a homemade sandwich, or sugary drink for water. Start with one change and add more as it becomes a habit
- Weekly check-ins on the percentage of ultra-processed foods eaten. Set a goal to reduce by 5% each month. If trying to conceive, track this alongside fertility tracking apps. After 3 months, reassess and set new goals. Share progress with your partner since both parents’ diets matter
This research suggests an association between ultra-processed food consumption and fertility and early pregnancy outcomes, but does not prove cause and effect. These findings come from a relatively healthy population in the Netherlands and may not apply to all groups. If you’re having trouble getting pregnant or have concerns about your pregnancy, consult with your doctor or fertility specialist. Dietary changes should be discussed with a healthcare provider, especially if you have existing health conditions. This information is for educational purposes and should not replace professional medical advice.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.