The study, published this month in the journal Cell Metabolism, followed 43 men, ages 20 to 35, who each spent three weeks on both a highly processed and minimally processed diet. The ultra-processed plan included ready-to-eat meals, sweetened cereals, processed meats such as sausage and cold cuts, packaged breads and snacks, flavored yogurts and soft drinks. The whole-foods diet featured fresh fruits and vegetables, eggs, meat, fish, whole grains, legumes, plain dairy products and nuts and seeds.
Even with identical calorie intake, men on the ultra-processed diet gained about 2 pounds of fat mass and showed worse heart-health markers than during the unprocessed phase. The researchers noted that the differences in body weight suggest that calories from unprocessed and ultra-processed foods are not equally stored or metabolized, even when controlled for macronutrient load. The study also found that participants on the ultra-processed diet had higher levels of pollutants known to affect sperm quality, including a plastics-related phthalate chemical called cxMINP. They also showed decreased levels of testosterone and follicle-stimulating hormone (FSH), both key to sperm production.
David Shusterman, a board-certified urologist, commented that the study adds an important piece to a growing body of literature linking diet quality — not just calories — to men’s metabolic and reproductive health. Meanwhile, the researchers acknowledged that the study — which did not include women or older adults — relied on participants accurately following and reporting their diets, potentially introducing bias. The three-week duration may also have been too short to show the full long-term effects of processed versus unprocessed foods, they noted.
Dr. Justin Houman, a urologist at Cedars-Sinai Medical Center in Los Angeles, cautioned that the results shouldn’t be applied to older men or those with health issues. While short-term drops in testosterone and sperm quality don’t prove infertility, they indicate early changes that warrant further research. Houman noted that controlled studies limit overeating, and the effects could be worse in real life. ‘In the wild, ultra-processed foods also drive higher calorie intake, so real-world effects could be larger, not smaller,’ he told Fox News Digital.
He added that some convenience foods can still fit into a healthy diet, especially when they are low in additives and high in fiber and protein. ‘I’m not telling patients to fear every wrapper, but I am advising men who care about testosterone, body composition and sperm quality to make minimally processed foods their default and treat UPFs, including protein bars, as occasional tools, not staples,’ he said.