March 25, 2026, 8:24 pm | Read time: 8 minutes
Frequent consumption of fast food and heavily processed foods could impair fertility. A recent study shows: High consumption of ultra-processed foods was linked to lower fertility, especially in men. Researchers also found evidence of negative effects for women—particularly in early embryonic development.
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According to the Federal Institute for Population Research, nearly one in three women of reproductive age in Germany is affected by pregnancy loss or infertility.1 Infertility describes the occurrence of problems when trying to conceive, resulting in delayed or no pregnancy. About nine percent of women reported experiencing one or more miscarriages. Men are also increasingly facing challenges in conceiving. Sperm quality in men has been steadily declining for years, as FITBOOK has previously reported. A recent study from the Netherlands has now examined the role of fast food in the fertility of men and women.2 It found that higher consumption of heavily processed foods was associated with a lower likelihood of becoming pregnant in a given month.
What Exactly Was Examined in the Fast-Food Study?
Researchers from the Erasmus Medical Center and Erasmus University Rotterdam, along with the Dutch Health and Research Organization, studied how the consumption of ultra-processed foods like fast food, ready-made products, snacks, and soft drinks affects fertility in men and women, as well as early embryonic development. They used data from the Generation-R-Next cohort.
The Generation-R-Next study is a large, ongoing investigation that follows couples from pre-conception through the early years of their children’s lives. It examines 831 women and 651 of their male partners. All participants completed a detailed dietary questionnaire at the beginning of pregnancy.
Participants had to report what they had eaten in the previous four weeks, considering more than 200 foods. Researchers then classified each food using a known classification system based on how industrially processed it was. The most processed foods had the following characteristics:
- high in added sugar
- high in unhealthy fats
- very salty
- contained chemical additives
- low in fiber
- lacking nutrients
The team then calculated what percentage of each person’s total daily food intake came from ultra-processed foods.
Additionally, standardized ultrasound measurements were used to assess early embryonic development in pregnant women. This included measuring embryo length and yolk sac volume around the 7th, 9th, and 11th weeks of pregnancy.
How Fast Food Affects Fertility
Data analysis revealed that the median consumption of ultra-processed foods accounted for 22 percent of women’s total food intake. For men, the figure was 25.1 percent, indicating that men generally ate less healthily. Interestingly, these numbers were below the national average in the Netherlands, as researchers noted. In some countries, the proportion of ultra-processed foods is about 50 to 60 percent of daily calories.
The second finding: Men with higher consumption of ultra-processed foods had a significantly increased risk of being classified as subfertile. Subfertility refers to reduced fertility or conception ability over a certain period.
Men in the highest quartile of unhealthy food intake had a 69 percent higher likelihood of being classified as subfertile compared to men in the lowest quartile. These associations persisted even after researchers accounted for a long list of potential confounding factors. In other words, the higher the fast-food consumption in men, the stronger the link to infertility. For women, however, there was no clear connection between fast-food consumption and fertility or pregnancy occurrence.
Also interesting: When exercise positively affects women’s fertility—and when it doesn’t
Fast-Food Consumption Also Affects Embryonic Development
However, researchers identified a different impact of unhealthy foods on pregnant women. Higher consumption of ultra-processed foods was associated with shorter embryo length and smaller yolk sac volume around the 7th week of pregnancy.
Specifically, the reduction in embryo length was 0.13 standard deviations per unit increase in processed food intake. The decrease in yolk sac volume was 0.14 standard deviations per unit increase. For women in the highest quartile of fast-food consumption, yolk sac volume in the seventh week was 0.41 standard deviations lower than for women in the lowest quartile.
In contrast, men’s diets were not noticeably linked to embryo length or yolk sac volume. This suggests a more direct influence of maternal diet in the first trimester.
Interestingly, these effects on early growth were particularly measurable in the 7th week, while they diminished in the 9th and 11th weeks. This indicates that maternal nutrition plays a critical role, especially in the very first phase of organ development.
Why Does Fast Food Affect Fertility?
Although the study does not provide a clear explanation for these links between fast food and fertility, the researchers have some hypotheses. According to them, ultra-processed foods contain high levels of sugar, refined starch, unhealthy fats, salt, and additives. At the same time, they provide few micronutrients and fiber. This combination promotes obesity, insulin resistance, and systemic inflammation, which can disrupt hormone balance and spermatogenesis in the body. This could, for example, lower testosterone levels and increase oxidative stress in the testes.
For sperm, adequate amounts of antioxidants like vitamins C and E, folate, unsaturated fatty acids, and trace elements are necessary. Additionally, many fast-food items come into contact with packaging that contains hormone-active chemicals. These can interfere with the reproductive axis.
For women, the embryo’s nourishment in early pregnancy initially depends almost entirely on the yolk sac. Poor nutrient quality in the maternal diet could impair its function and slow early growth.
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Limitations of the Study
This investigation is a prospective observational study. It cannot establish hard causal relationships, only associations. Additionally, participants were predominantly well-educated and nutritionally healthier. Therefore, the results are not easily transferable to other unhealthy population groups. And, of course, participants’ self-reported dietary information is prone to error and may only reflect a snapshot of regular eating habits.
However, this is not the first study to show the impact of unhealthy diets on fertility, especially in men. A Danish study from 2025 already found that ultra-processed foods in men not only lead to weight gain but also disrupt hormone balance and release harmful substances. This, in turn, could lead to a long-term deterioration in sperm quality. FITBOOK has previously reported on this.
Experts Interpret the Results
In addition to the study results, specialists have assessed the role of diet and lifestyle in fertility—and see clear connections.
Diet and Weight as Central Factors
Gynecologist Dr. Heidi Goesslinghoff confirms from her practice experience: “These studies align with my experience and, of course, with what I have observed in practice. Diet is a very important part of unfulfilled desire for children.” Obesity can affect the cycle and disrupt ovulation.
She also points to inflammatory processes: “Additionally, adipose tissue produces pro-inflammatory messengers like TNF-α and interleukins. These can lead to oxidative stress and also disrupt egg maturation and implantation.” This can also have negative effects on men—such as on sperm motility and genetic material.
Even moderate changes show effects, according to Goesslinghoff: “For women, a weight reduction of five to ten percent can already have a significant effect on the cycle with a better chance of pregnancy.”
Age and Biological Limits
Another aspect is age: “Another factor that significantly complicates pregnancy and increases the rate of miscarriages is the fact that most women are much older at the time of their first child than they were ten years ago.” This increases the risk of chromosomal abnormalities in both eggs and sperm.
Declining Sperm Quality Observed for Years
Urologist Christoph Pies also sees the study findings confirmed by his experience: “Absolutely. A decline in sperm quality over the past decades is well-documented in the literature.” This trend is also evident in everyday practice. He emphasizes that the causes are not attributable to a single factor but result from a combination of various influences.
Diet as a Decisive Influence Factor
According to Pies, diet plays a central role: “Yes, through various mechanisms.” Ultra-processed foods are particularly in focus, as they often contain high amounts of sugar, refined carbohydrates, and unhealthy fats, while lacking essential nutrients.
This combination can disrupt metabolic processes and hormone balance. Certain fats promote inflammatory processes in the body and can affect sperm structure. The absence of protective nutrients also increases susceptibility to oxidative stress, which further damages cells.
Many Other Risk Factors in Combination
Additionally, Pies mentions a range of other influencing factors: “In today’s world, Western societies are exposed to a multitude of potentially harmful influences.” These include diet, smoking, alcohol, lack of exercise, and obesity.
There are also physical and external factors like hormonal disorders, aging, chronic inflammation, and environmental pollutants—such as chemicals, pesticides, plasticizers, air pollution, or heat. Possible effects of electromagnetic radiation are also discussed, although the study situation here is not clear.