Could your diet before conception shape fertility and early development? New research reveals sex-specific links between ultraprocessed foods, reduced fertility in men, and subtle changes in early embryonic growth.
Study: Periconceptional ultra-processed food consumption in women and men, fertility, and early embryonic development. Image credit: Pressmaster/Shutterstock.com
Ultraprocessed food (UPF) consumption is linked to poor health outcomes. However, periconceptional UPF exposure may influence very early development, with potential implications across the life course. A study published in Human Reproduction found that higher UPF intake around conception was associated with reduced fecundability and higher subfertility risk in men and showed limited inverse associations with early embryonic growth, strongest at 7 weeks.
Ultraprocessed food diets in high-income populations
The period surrounding conception is crucial. Events occurring during this window can influence embryonic development and infant health. Rapid embryonic growth is a marker of healthy development, while impaired growth increases the risk of adverse pregnancy outcomes such as low birth weight, preterm birth, and childhood cardiovascular risk.
Embryonic growth includes the growth of the fetal pole and the yolk sac, which nourishes the embryo until placental function is established. Poor yolk sac growth may increase the risk of miscarriage and preterm birth, highlighting the importance of identifying modifiable risk factors.
Parental diet is a major risk factor for such events. UPFs (nutrient-poor, industrially manufactured products high in sugar, salt, unhealthy fats, and additives) can contribute up to 60 % of daily energy intake in some wealthy countries. High maternal UPF consumption is linked to adverse pregnancy and offspring health outcomes, including gestational diabetes and hypertension, and infant adiposity.
Despite this, no studies have examined the combined effects of parental UPF consumption around the time of conception on fertility outcomes and early embryonic development, motivating this study.
Food frequency data captures periconceptional ultraprocessed intake
This research formed part of the Generation R Next Study, a population-based prospective cohort study beginning before conception and continuing into childhood. The study aims to identify preconceptional and early-pregnancy factors that affect fertility, embryonic development, and childhood health and development.
Fertility analyses included 831 women and 651 male partners randomly selected from the larger cohort. Embryonic growth assessment was performed in 704 women and 537 male partners. All were attempting conception or were already pregnant.
Participants completed a food frequency questionnaire at a median of 12 weeks of gestation to quantify their periconceptional dietary habits. UPFs were identified by the NOVA classification and expressed as a proportion of total food intake.
Fertility metrics included time to pregnancy, mode of conception, fecundability (probability of conceiving within one month), and subfertility (taking more than 12 months to conceive, or using assisted reproductive technology, ART).
Embryonic growth was examined by transvaginal ultrasound at 7, 9, and 11 weeks of gestation. The crown-rump length (CRL) and yolk sac volume were measured during each session. CRL refers to the length from the top of the fetal head to the buttocks in millimeters. Notably, the yolk sac typically regresses around 10 weeks of gestation.
Study findings
The median UPF intake was 22 % of total food intake (563 g/day) in women, versus 25 % (643 g/day) in men. Correlation within couples was low (r = 0.34), with 57 % of couples reporting discordant consumption. Only 12 % of couples had high UPF intake, while 31 % had a low intake.
Maternal UPF intake
Women showed no association between UPF intake and fecundability. Only the third quartile of UPF consumption was linked to higher subfertility risk, though no dose-response pattern was observed.
The CRL was reduced at 7 weeks of gestation across the full range of increasing maternal UPF intake, though interquartile comparisons did not support this. This association weakened at 9 and 11 weeks of gestation.
Yolk sac volume was also smaller at seven weeks in the fourth quartile compared to the first (lowest) quartile, and across the full range, but not at later time points. Findings at later gestational ages should be interpreted cautiously, as these analyses are largely exploratory.
All associations were adjusted for potential confounding factors, including substance use, folic acid supplementation, nausea and vomiting, body mass index (BMI), education level, ethnicity, and age.
Paternal UPF intake
In men, higher UPF intake was linked to reduced fecundability (a 10 % decrease per standard deviation increase in UPF intake) and increased subfertility risk across the full range, but not in quartile-based comparisons.
The second and third quartiles of paternal UPF intake were associated with greater CRL at 9 weeks; however, this association was not supported in non-quartile-based analyses, and no association with yolk sac growth was observed, indicating no consistent relationship with embryonic development.
UPF intake among couples did not correlate with any of these outcomes, although the small number of couples with high UPF intake limited statistical power.
Nutrient-poor UPFs may drive oxidative stress and dysfunction
These associations persisted after adjusting for lifestyle, social, and demographic factors, and for the woman’s UPF consumption, and were observed at relatively low levels of UPF intake. Though not a focus of this study, the authors propose hypothesized potential mechanisms for these associations.
Firstly, many UPFs have a poor nutritional profile, potentially triggering oxidative stress, high testosterone levels in men, and potential mitochondrial dysfunction, potentially impairing sperm motility.
Secondly, UPF packaging often contains endocrine disrupters such as phthalates, which may affect male fertility and genes involved in yolk sac function. This would reduce nutrient production and transport to the embryo. Higher oxidative stress could also damage lipids and proteins, affecting early development.
The authors suggest that certain subgroups of UPF (such as artificially sweetened drinks and processed meats) are consistently linked to multiple adverse health outcomes. In contrast, processed bread and cereals do not show these associations. Importantly, breads constituted a major portion of UPF intake in this study.
Sex-specific dietary effects may inform fertility guidance strategies
Periconceptional UPF intake shows sex-specific associations; maternal intake is associated with very early embryonic growth, whereas paternal intake is linked to reduced fecundability and increased subfertility risk.
These findings underline the need for further research to validate these effects, identify underlying mechanisms, and assess potential effects on birth outcomes and long-term offspring health. This could shape prenatal care of both partners and guide public health strategies in this area.
Study limitations
The study sample comprised a healthy group of people, which limits the generalizability of the findings to individuals with high risk for subfertility or early pregnancy complications. As an observational cohort study, it cannot establish causality, and randomized controlled trials in diverse populations are needed.
The observed high subfertility rate among women and the inclusion of only pregnant couples suggest potential selection bias, as only couples who conceived were included due to dietary assessment occurring in early pregnancy, and the subfertility rate in the study population was higher than expected for the general population.
Ultraprocessed foods may influence fertility before conception
Maternal UPF intake showed limited inverse associations with embryonic growth, whereas paternal UPF intake was associated with reduced fecundability and increased subfertility risk. Future longitudinal studies are required to confirm these findings and identify their long-term impact.
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