Processed foods lower sperm quality and testosterone

A controlled dietary trial found that an ultra-processed diet altered reproductive hormones, worsened metabolic markers and produced signs of impaired sperm function in healthy young men.

Processed foods lower sperm quality and testosterone

Table of contents

    The same calories did not produce the same effects

    Calories and macronutrients are often treated as the main determinants of a diet’s health effects. A controlled dietary trial published in Cell Metabolism suggests that the degree of food processing may also matter, even when energy, protein, carbohydrate and fat intake are closely matched.

    Researchers compared diets rich in ultra-processed foods with diets based predominantly on unprocessed or minimally processed foods. The participants were healthy men between 20 and 35 years of age.

    After three weeks, the ultra-processed diet was associated with greater fat accumulation, changes in reproductive hormones and signals of poorer sperm function. These differences appeared even among participants whose calorie intake was adjusted to their estimated energy requirements.

    The findings do not mean that every packaged or processed product is harmful. The intervention concerned a dietary pattern dominated by ultra-processed foods, classified as NOVA group 4 products. These commonly contain industrial ingredients, flavourings, emulsifiers, stabilisers or other substances rarely used in a home kitchen.

    Study details

    The study was designed to separate the effects of food processing from the effects of simply eating more calories.

    • Publication title: Effect of ultra-processed food consumption on male reproductive and metabolic health
    • Authors: Jessica M. Preston, Jo Iversen, Antonia Hufnagel, Line Hjort, Jodie Taylor, Clara Sanchez, Victoria George, Ann N. Hansen, Lars Ängquist, Susan Hermann, Jeffrey M. Craig, Signe Torekov, Christian Lindh, Karin S. Hougaard, Marcelo A. Nóbrega, Stephen J. Simpson and Romain Barrès.
    • Publication date: 2025.
    • Journal: Cell Metabolism.
    • DOI: 10.1016/j.cmet.2025.08.004
    • Study design: Randomised crossover controlled dietary intervention.
    • Participants: 43 healthy men aged 20–35 years.
    • Dietary periods: Each participant followed an ultra-processed diet and an unprocessed diet for three weeks each.
    • Washout period: The two dietary interventions were separated by approximately three months.
    • Energy groups: One group received an energy intake adjusted to individual requirements, while another received approximately 500 additional kilocalories per day.
    • Diet matching: The ultra-processed and unprocessed diets were designed to provide comparable amounts of calories and macronutrients within each energy group.
    • Main outcomes: Body weight and composition, cardiometabolic markers, reproductive hormones, semen parameters and exposure to selected environmental contaminants.
    • Full publication: Cell Metabolism

    Because the same participants completed both interventions, researchers could compare how each man responded to the two dietary patterns rather than relying only on differences between separate groups.

    What happened to sperm quality and reproductive hormones?

    The study detected several changes suggesting that an ultra-processed dietary pattern can affect male reproductive biology within a relatively short period.

    Participants following the ultra-processed diet experienced lower concentrations of follicle-stimulating hormone, or FSH. This hormone plays an important role in supporting sperm production in the testes.

    Testosterone levels also decreased under some study conditions. However, the hormonal results were not uniform across every measurement and subgroup, so they should not be interpreted as proof that eating a single ultra-processed meal immediately suppresses testosterone.

    The semen analysis provided a similarly nuanced picture:

    • Total sperm motility decreased, indicating that a smaller proportion of sperm cells were moving normally after the ultra-processed dietary period.
    • Other sperm-quality measures showed signs of deterioration, although not every comparison remained statistically significant after adjustment for multiple testing.
    • The short duration of the intervention matters, because the complete development of human sperm takes considerably longer than three weeks. The study may therefore have captured acute changes in the reproductive environment rather than the full effect on a new generation of sperm cells.

    The most accurate conclusion is that the diet produced concerning reproductive changes and a trend toward impaired sperm quality, rather than proving permanent infertility.

    The ultra-processed diet also increased body fat

    The effects were not limited to reproductive health. Men accumulated approximately one kilogram more fat mass during the ultra-processed diet than during the unprocessed diet.

    Importantly, this difference appeared regardless of whether participants received an energy-balanced diet or an additional 500 kilocalories per day. This suggests that the results cannot be explained solely by intentional calorie overfeeding.

    Several cardiometabolic indicators also changed:

    • The LDL-to-HDL cholesterol ratio worsened, indicating a less favourable lipoprotein profile.
    • Body weight and fat mass increased more during the ultra-processed phase, despite matching the diets for calories and macronutrients.
    • Hormones involved in appetite, metabolism and energy balance changed, suggesting that processing may affect how the body handles and responds to food.

    The study does not establish one definitive mechanism. It does, however, challenge the idea that two diets with the same calorie and macronutrient content must have identical physiological effects.

    Why could ultra-processed foods have different effects?

    Ultra-processing changes more than the nutrition label. It can alter the physical structure of food, eating speed, nutrient absorption and exposure to additives or contaminants.

    Several mechanisms could have contributed to the findings.

    Changes in the food matrix

    Grinding, extrusion, refining and other industrial processes can break down the natural structure of food. This may affect digestion speed, satiety and the amount of energy absorbed, even when the calculated calorie content is similar.

    Different combinations of ingredients

    Ultra-processed products frequently contain refined starches, isolated proteins, added sugars, industrial fats, emulsifiers and flavour enhancers. The biological effects of this combination may differ from those of intact foods such as vegetables, legumes, whole grains, eggs, fish or fresh meat.

    Exposure to endocrine-disrupting chemicals

    Researchers found increased exposure to cxMINP, a metabolite associated with phthalates used in plastics. Higher levels were detected during the ultra-processed dietary period.

    Phthalates can enter food during manufacturing, processing, storage or contact with packaging. Some compounds in this group can interfere with hormonal signalling, although this study cannot prove that cxMINP directly caused the observed reproductive changes.

    Micronutrient and bioactive differences

    Even when calories and macronutrients are matched, diets may still differ in fibre, micronutrients, phytochemicals and other bioactive compounds. These differences can influence the gut microbiome, inflammation, oxidative stress and hormonal regulation.

    What the study does not prove

    The controlled design makes this study more informative than a simple observational association, but its results still require careful interpretation.

    Several limitations reduce how broadly the findings can be applied:

    • The study included only 43 participants. A crossover design improves statistical efficiency, but the sample remains relatively small.
    • All participants were healthy young men. The findings may not apply directly to women, older adults, people with obesity or men already experiencing fertility problems.
    • Each dietary phase lasted only three weeks. This was sufficient to detect acute physiological changes but not long-term clinical outcomes.
    • Sperm development takes longer than the intervention. A longer study would be required to determine the complete effect on spermatogenesis and fertility.
    • Not every semen parameter changed significantly. Some results represented directional trends rather than definitive evidence of clinically meaningful impairment.
    • The study examined an entire dietary pattern. It cannot identify one additive, ingredient, package or processing method as the sole cause.
    • The findings do not show that occasional consumption causes infertility. They concern a diet in which ultra-processed foods constituted a major proportion of intake.

    The title’s reference to lower sperm quality therefore describes the overall direction of the findings. It should not be interpreted as evidence that all processed food inevitably or permanently reduces male fertility.

    What this means in practice

    The study supports focusing not only on calories and macronutrients but also on what foods are made from and how extensively they have been processed.

    A practical response does not require eliminating every packaged product. Processing exists on a spectrum, and foods such as frozen vegetables, plain yoghurt, canned legumes or minimally processed whole-grain products can still form part of a nutritious diet.

    The more relevant goal is to prevent ultra-processed products from becoming the foundation of daily eating. This can be achieved by prioritising:

    • Meals built around recognisable whole-food ingredients, including vegetables, fruit, legumes, whole grains, eggs, fish, dairy products and minimally processed meat.
    • Products with shorter and more familiar ingredient lists, particularly when choosing foods eaten every day.
    • Home-prepared meals when practical, which provide greater control over ingredients and reduce reliance on industrial formulations.
    • Dietary quality in addition to calorie tracking, because matching energy intake alone may not produce equivalent metabolic effects.
    • A balanced interpretation of individual foods, rather than labelling every form of processing as equally harmful.

    For men concerned about fertility or testosterone, diet is only one part of a larger picture that also includes body composition, sleep, physical activity, alcohol, smoking, heat exposure, medication use and underlying medical conditions.

    The central message from this trial is not that calories no longer matter. It is that calories may not tell the whole story.

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