Even low-calorie processed food causes weight gain, testosterone loss in men, study suggests

Not all calories are created equal, and some could do far greater harm to men's health, new research suggests.
A small study led by a team from the University of Copenhagen in Denmark suggests that ultra-processed foods (UPFs) may negatively affect men's metabolism and fertility even when calorie, protein, carbohydrate and fat intake are the same as a whole-food diet.
The research, 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.
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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.
"Differences in body weight between the two diets suggest that calories from unprocessed and ultra-processed foods are not equally stored or metabolized, even when controlled for macronutrient load," the scientists wrote.
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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.
The study sheds light on whether the harmful effects of processed foods come from their industrial nature or simply from causing people to overeat.
"Our results prove that ultra-processed foods harm our reproductive and metabolic health, even if they're not eaten in excess," Jessica Preston, lead author of the study, said in a news release from the Novo Nordisk Foundation, which provided funding for the research.
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The researchers wrote that eating ultra-processed food is "detrimental for cardiometabolic and reproductive outcomes, regardless of excessive caloric intake."
Dr. David Shusterman, a board-certified urologist and chief physician at Modern Urologist in New York City, said the study, which he was not involved with, adds an important piece to a growing body of literature linking diet quality — not just calories — to men's metabolic and reproductive health.
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Adult obesity has more than doubled since 1990, according to the World Health Organization (WHO). Studies have also found that sperm count, motility, concentration and volume have declined sharply in recent decades.
Meanwhile, ultra-processed foods now make up more than half of the average American diet, according to the Centers for Disease Control and Prevention (CDC).
"We were shocked by how many body functions were disrupted by ultra-processed foods, even in healthy young men," the study's senior author, Romain Barrès, said in the release. "The long-term implications are alarming and highlight the need to revise nutritional guidelines to better protect against chronic disease."
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The researchers added that shifting dietary habits away from ultra-processed and toward less-processed foods may also benefit mental health.
They noted that the study — which did not include women or older adults — relied on participants accurately following and reporting their diets, potentially introducing bias.
"While the sample is small and the intervention short, the results signal that food processing itself may carry endocrine and fertility risks worth paying attention to," Shusterman said.
The three-week duration may also have been too short to show the full long-term effects of processed versus unprocessed foods, the researchers noted.
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Fox News Digital has reached out to the researchers for comment.
Dr. Justin Houman, chief clinical officer at Bastion Health and a urologist at Cedars-Sinai Medical Center in Los Angeles, said the results also shouldn't be applied to older men or those with health issues yet.
While short-term drops in testosterone and sperm quality don't prove infertility, they indicate early changes that warrant further research, he said.
Houman, who was not involved in the study, 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.
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