Unpacking the Link Between Ultraprocessed Foods and Reproductive Health

Recent research from two separate studies has explored potential associations between the consumption of ultraprocessed foods (UPFs) and various reproductive outcomes, including fertility rates and early embryonic development, in both men and women. These investigations contribute to a growing body of knowledge regarding how dietary habits may relate to reproductive health.

These new studies add to a growing understanding of how what we eat could impact the ability to conceive and the earliest stages of human development.

Parental Ultraprocessed Food Intake and Embryonic Development

A study, part of the Generation R Next Study and published in Human Reproduction, investigated connections between ultraprocessed food (UPF) consumption around the time of conception and sex-specific outcomes in fertility and early embryonic development.

• The research analyzed data from 831 women and 651 male partners for fertility outcomes, and 704 women and 537 male partners for embryonic growth.
• Participants were either attempting conception or were already pregnant and completed a food frequency questionnaire at a median of 12 weeks of gestation.
• UPFs were identified using the NOVA classification.
• Fertility metrics included time to pregnancy, mode of conception, fecundability (probability of conceiving within one month), and subfertility (taking over 12 months to conceive or using assisted reproductive technology, ART).
• Embryonic growth was assessed via transvaginal ultrasound at 7, 9, and 11 weeks of gestation, measuring crown-rump length (CRL) and yolk sac volume.

The median UPF intake among participants was 22% of total food intake for women (approximately 563 g/day) and 25% for men (approximately 643 g/day). The correlation of UPF intake within couples was noted as low.

• No direct association was found between maternal UPF intake and fecundability.
• However, the third quartile of UPF consumption was linked to a higher risk of subfertility, although a clear dose-response pattern was not identified.
• Maternal UPF intake showed limited inverse associations with crown-rump length (CRL) at 7 weeks and smaller yolk sac volume at 7 weeks, with these associations weakening at later gestational ages.

• Higher UPF intake in men was associated with reduced fecundability (a 10% decrease per standard deviation increase in UPF intake) and an increased risk of subfertility.
• No consistent relationship between paternal UPF intake and embryonic development was observed in this study.

Ultraprocessed Foods and Female Fertility

Separately, research originating from McMaster University, published in Nutrition and Health, examined a potential correlation between the consumption of ultraprocessed foods and lower fertility rates in women.

This independent study highlights a significant association between higher UPF intake and reduced fertility odds in women.

• This study analyzed data from over 2,500 women who participated in the National Health and Nutrition Examination Survey (NHANES).
• Data collection for the survey included interviews, 24-hour dietary recalls, and laboratory tests, covering diet, demographics, health status, and biomarkers.
• Health factors such as age, weight, and lifestyle were considered.

• The study observed that women who reported difficulty conceiving after a year had daily diets comprising approximately 31% UPFs.
• These women also demonstrated lower consumption of fruits, vegetables, whole grains, and healthy fats.
• Data indicated that a higher intake of ultra-processed foods was linked to approximately 60% lower odds of fertility in this group.

Proposed Mechanisms

Researchers involved in both studies have suggested several potential mechanisms that could explain these observed associations:

The poor nutritional quality and presence of harmful chemicals in UPFs are hypothesized to interfere with key reproductive processes.

• The poor nutritional profile commonly found in many UPFs may contribute to oxidative stress and potential mitochondrial dysfunction. In men, this could lead to elevated testosterone levels and impaired sperm motility.
• Chemicals, such as phthalates, BPA, and acrylamides, are frequently found in UPF packaging or transferred from processing equipment. These substances are recognized as potential hormone disruptors, which may affect male fertility and genes involved in yolk sac function, potentially reducing nutrient transport to the embryo.
• Ultra-processed items often contain high levels of sugar, saturated fat, and salt, while frequently lacking essential vitamins and fiber, which could impact overall reproductive health.

Limitations and Future Research

Both studies acknowledge several limitations inherent to their methodologies:

As observational studies, these investigations can only identify correlations, not direct cause-and-effect relationships.

• As observational studies, they identify correlations rather than establishing direct causation.
• The sample population of the Human Reproduction study comprised a healthy population, which may limit the generalizability of the findings to individuals with high risk for subfertility or early pregnancy complications.
• Potential selection bias was noted in the Human Reproduction study due to the inclusion of only couples who conceived and a higher-than-expected subfertility rate in the study population.

The findings highlight a need for further research to validate these effects, understand the underlying mechanisms, and assess potential long-term impacts on birth outcomes and offspring health. Such research could inform prenatal care for both partners and guide public health strategies regarding dietary recommendations.