Ultra-Processed Foods Cut Sperm Motility 18% in Just Three Weeks

Three weeks on an ultra-processed food diet reduced sperm motility by approximately 18% and testosterone by roughly 11% in a controlled trial of healthy young men — without the men eating a single extra calorie. The harm came from the food itself, not from overeating.

What the Study Actually Found

Researchers at the University of Copenhagen randomized 43 healthy men, ages 20–35, into a two-arm crossover trial: three weeks on an ultra-processed food (UPF) diet, then three weeks on an unprocessed whole-foods diet (with a 12-week washout between arms). The UPF diet derived roughly 77% of calories from ultra-processed foods; the unprocessed diet derived just 1%. Published in Cell Metabolism, the trial tested two caloric conditions — maintenance calories and excess calories — to separate the effect of the food type from the effect of overeating.

In the excess-calorie arm, men saw approximately 18% decreased sperm motility, a 14% drop in follicle-stimulating hormone (FSH), and elevated urinary levels of cxMINP — a phthalate metabolite found in plastic food packaging. An 11% testosterone decline trended toward significance in the maintenance-calorie arm. Cardiometabolic markers worsened regardless of caloric condition: body weight increased, and the LDL:HDL ratio deteriorated even in men eating only what they needed.

That last finding is the study’s most consequential insight. The reproductive and metabolic damage appeared even when men consumed maintenance calories — which rules out the easy explanation that ultra-processed food causes harm only because it drives overeating. The researchers propose that something specific to UPFs is exerting independent biological effects: additives, emulsifiers, processing byproducts, or plasticizer contamination from packaging.

Why the Plastic Packaging Finding Changes the Frame

The elevated cxMINP levels are not a minor footnote. Phthalates — the class of plasticizers found in flexible food packaging — are documented endocrine disruptors that interfere with testosterone synthesis and spermatogenesis. The researchers wrote explicitly that the presence of cxMINP at higher levels after UPF consumption “suggests that contaminants from packaging or processing may be leaching into the food supply.” If that mechanism holds under further study, the implication extends well beyond caloric quality: even “healthy” ultra-processed food — low-calorie, minimally sugared — may carry a packaging-contaminant burden that affects hormonal function.

This sits against a troubling backdrop. Global sperm counts have declined roughly 60% since the 1970s, a trend documented across populations and decades that cannot be fully explained by lifestyle factors alone. Environmental and dietary contaminants have long been the leading candidate for the residual variance — and this study adds a randomized, controlled data point linking a specific dietary pattern to measurable reproductive endpoints.

A separate 2026 cohort study in Human Reproduction, embedded in the Generation R Next Study in Rotterdam, tracked couples actively trying to conceive and found that men’s higher UPF intake was associated with greater subfertility risk and longer time-to-pregnancy. Women’s UPF consumption during the periconceptional period correlated with slightly smaller embryonic growth at 7 weeks. Both sexes, both sides of conception — the signal is consistent.

The three-week intervention window in the Cell Metabolism trial deserves a caveat. Spermatogenesis takes 2–3 months, which means the study likely captured early, potentially reversible changes rather than the full biological impact of sustained UPF consumption. Whether longer exposure causes permanent damage — or whether dietary reversal quickly restores function — remains an open research question.

Source: Peter Attia MD

Content created with AI assistance and reviewed for accuracy.