Over recent decades, people's eating habits have undergone a profound shift, with ultra-processed foods (UPFs) becoming a daily staple for millions, especially in the developed world. Amid the pace and demands of modern life, the convenience of fast food has further enhanced its appeal.
Consumption has now risen to unprecedented levels, especially in high-income countries, where UPFs can make up a big proportion of someone’s daily diet. Unfortunately, scientific evidence is beginning to reveal an expanding range of health consequences linked to these foods, from the more commonly known obesity and chronic illness, to more sensitive issues including fertility and foetal health.
UPFs are industrial food products that undergo multiple stages of processing and often contain additives such as preservatives, artificial flavourings, colourings, and refined sugars and fats. They are usually ‘ready to eat’ or require only minimal preparation, but are typically poor in essential nutrients such as fibre, vitamins, and minerals. Examples include burgers, pizza, fried chicken, ready meals, instant noodles, potato crisps, biscuits, cakes, and soft drinks such as industrially produced fruit juices high in sugar.
Charting the impact
A study of 831 women and 651 male partners, published in March in the journal Human Reproduction, adopted a longitudinal design and followed a large cohort of couples from pre-conception through the earliest stages of pregnancy. Its aim was to clarify the relationship between diet, fertility, and embryonic development.
Researchers gathered data on dietary habits, tracked time to conception (as an indicator of fertility), and performed ultrasound scans to measure embryonic growth and yolk sac size in the seventh, ninth, and eleventh weeks. The findings suggest that UPFs may have a direct and noticeable effect on male fertility, with higher consumption associated with reduced fertility and a longer time to conception.
Some think this stems from sperm's sensitivity to dietary quality. Foods rich in unhealthy fats, sugars, and additives can impair sperm quality, count, and motility, while also contributing to increased inflammation and oxidative stress in the body, both of which are widely recognised for their harmful effects on reproductive health. Taken together, it suggests that a man’s diet plays a central role in fertility, with practical implications for couples hoping to conceive.
Among women, the study found no direct association between UPF consumption and reduced fertility or delayed conception, but it did reveal early effects on embryonic development. The embryos of women who consumed more UPFs were found to grow at a slightly slower rate, with a smaller yolk sac—the essential structure that nourishes the embryo during the first weeks of pregnancy.
Although the differences may appear slight, their implications are not. They suggest that the mother’s diet may shape the womb's internal environment from the earliest stages, with possible consequences for the embryo’s later health and development.
The yolk sac plays a vital role in early pregnancy, as the first structure to nourish the embryo before the placenta is fully formed. It supplies essential nutrients and oxygen, supports the production of early blood cells, and contributes to the initial development of organs. Its size and shape are among the key indicators physicians rely on when assessing the health of a pregnancy in its earliest weeks. Any change in its size or function, however subtle, may have an early influence on embryonic development.
