September 3, 2025, 11:09 am | Read time: 5 minutes
Highly processed foods may be responsible for the worldwide decline in sperm quality. This is the finding of a new study from Denmark. An unhealthy diet has a far more dramatic impact on men’s metabolism and hormone systems than previously thought.
The decline in sperm quality among men is a global phenomenon that researchers have been observing for about 50 years. However, the exact causes remain largely unclear. A small but thorough study, in which the University of Copenhagen was significantly involved, has now discovered new clues. According to the study, highly processed foods not only lead to weight gain in men but also disrupt hormone balance and release harmful substances, which in turn lead to a long-term deterioration in sperm quality. The study was published in the journal “Cell Metabolism.”1
Highly Processed Foods–A Stealthy Threat to Health and Reproductive Ability?
Ready meals, fast food, snacks, sausage, industrially produced baked goods, soft drinks, and the like—a large portion of people consume these products daily. They often make up half of the meals. And even though research has impressively shown that these highly processed foods can be responsible for 32 health problems, including type 2 diabetes and obesity, it does not change their popularity.
Now, another study on this topic has emerged, which should particularly alert men: Their sperm quality is at risk. And not only that: The type of diet also leads to a higher concentration of a chemical in the body that is found in plastics and food packaging.
Study with 43 Young, Healthy Men
To find out the effects of highly processed foods on male metabolism and fertility, including sperm quality, the research team recruited 43 healthy men aged 20 to 35. They were divided into groups with the following study design:
- Each participant completed two dietary phases of three weeks each. One phase with predominantly highly processed foods and one with predominantly unprocessed foods. The calorie count remained constant.
- There was a three-month break in between, during which participants returned to their usual diet.
- In one phase, participants received approximately 500 additional calories to also examine the effect of a moderate calorie surplus.
- Sperm quality, blood, and hormone levels of all men were measured before and after each trial period.
How Highly Processed Foods Affect Male Health
After the evaluation, the researchers arrived at a series of somewhat surprising findings. It is often said: A calorie is a calorie. However, this does not seem to be the case with highly processed foods. Men who consumed them gained about one kilogram more fat mass compared to an unprocessed diet, regardless of whether they ate normally or with excess calories. The scientists also noted a concerning increase in a hormone-disrupting phthalate in both groups. This substance (plasticizer) is used in plastics, especially in packaging. Additionally, testosterone and follicle-stimulating hormone levels, which are crucial for sperm production, decreased in these men. The overall motility of the sperm also tended to decrease–an indication of a beginning qualitative impairment. However, this was not yet statistically significant, which could be due to the short trial period. It was also evident that a diet with highly processed foods led to a slight increase in certain inflammatory markers and cholesterol levels in the blood.
Researchers Alarmed by Results
“We were shocked at how many body functions are disrupted by highly processed foods, even in healthy young men. The long-term effects are alarming and underscore the need to revise dietary guidelines,” explains study leader Prof. Romain Barrès in a university statement.2 For the researchers, it is clear: Highly processed foods lead to an accumulation of harmful substances in the blood, negatively affecting sperm quality and testosterone levels. At the same time, they promote obesity, even when counting calories. An unprocessed meal, with the same energy density, is far less likely to add to the waistline. And this becomes apparent in a short time.
Reduced Fertility with This Diet
Sperm Quality in Men Continues to Decline–Here’s Why
What Makes Highly Processed Foods So Harmful? The Study Leader Explains
What exactly makes ready-to-eat snacks and the like so problematic for our health? And could they possibly also contribute to fertility problems in women? FITBOOK asked study leader Prof. Romain Barré. His assessment: “It’s a combination of several factors. Quickly eaten and just as quickly digested, glucose enters the bloodstream faster. This, in turn, promotes fat storage. Added to this are too many saturated fats, cholesterol, salt, and toxic substances, which, as our study has shown, negatively affect the hormone system.” For this reason, the researcher believes that highly processed foods could also impair female reproductive ability. Couples hoping to conceive should spend their waiting time at farmers’ markets and cooking together. With enjoyment and fresh foods, success might come sooner than expected.
Authors’ Conclusion
However, the team also notes that the study duration of a few weeks may not be sufficient to achieve results on long-term effects. It is also conceivable that certain values may normalize again. Nonetheless, they are confident that a diet primarily consisting of unprocessed foods brings only advantages in the long term and can positively impact male fertility.