An experimental study investigating the health effects of a three-week ultra-processed food diet found that such a diet impairs both metabolic and reproductive health compared to a diet based on unprocessed foods. The negative effects of ultra-processed food diets were independent of total caloric intake. The paper was published in cell metabolism.
Ultra-processed foods are industrial preparations made primarily from refined raw materials and additives rather than natural foods. In NOVA’s food classification system, these are the most highly processed food categories.
Ultra-processed foods typically contain substances such as refined sugars, hydrogenated oils, starches, and isolated proteins. It also contains additives such as preservatives, flavor enhancers, artificial colors, and emulsifiers designed to improve taste and shelf life. Common examples include packaged snacks, sugary drinks, instant noodles, processed meats, and ready-to-eat foods.
Ultra-processed foods are typically convenient, palatable, and actively marketed. They tend to be energy dense, low in nutritional value, and limited in fiber, vitamins, and minerals. Studies have shown that people who consume large amounts of these foods have an increased risk of obesity, cardiovascular disease, and metabolic disorders. Some authors suggest that a diet centered on ultra-processed foods can lead to a health condition called food addiction.
Study author Jessica M. Preston and colleagues wanted to compare the effects of a diet of ultra-processed foods and a diet of unprocessed foods on metabolic and male reproductive health. They conducted an experimental cross-over study in which 43 healthy young men (20 to 35 years old) followed a prescribed diet.
All participants followed the two diets for 3 weeks each. One group started on an ultra-processed diet and switched to an unprocessed diet, and the other group started on an unprocessed diet and switched to an ultra-processed diet. The study authors included a 12-week washout period between the two diets to allow residual effects to dissipate before participants started the second diet.
To separate the effects of calories and food quality, half of the participants ate a diet with enough calories to maintain their weight, and the other half ate a diet with excess calories (an additional 500 calories per day).
The two diets were precisely calibrated to have the same amount of carbohydrates, protein, and fat. However, ultra-processed food diets are designed to reflect the typical Western diet. Compared to unprocessed diets, they had higher contents of saturated fat, cholesterol, refined grains, added sugars, and dairy products, and lower amounts of fiber. In ultra-processed foods, 77% of calories came from ultra-processed foods, compared to less than 1% in unprocessed foods. The study authors provided all food to the participants for the duration of the study.
Study participants visited the center seven times: once for eligibility assessment, twice before starting the diet, twice after the diet, and twice during the washout period. During each pre- and post-diet visit, participants completed a questionnaire, underwent physical and vital sign measurements, completed a dual-energy X-ray absorptiometry (DXA) scan, and provided blood and semen samples.
The results showed that even when calories were strictly controlled, participants gained 1.3 to 1.4 kilograms more after the ultra-processed food diet than after the unprocessed food diet. More specifically, participants’ lean muscle mass did not change significantly between the two conditions, but their fat mass increased by approximately 1 kg after the ultra-processed food diet.
A diet of ultra-processed foods also had a negative impact on metabolic health indicators. Total cholesterol was higher and the ratio of low-density lipoprotein (LDL) to high-density lipoprotein (HDL) was increased, which was mainly seen in the calorie-adequate group. In the excess calorie group, a diet of ultra-processed foods was associated with increased diastolic blood pressure.
Importantly, the diet also had negative effects on men’s reproductive health. Eating ultra-processed foods tended to reduce follicle-stimulating hormone (FSH) levels in the calorie-excess group and reduce circulating testosterone in the calorie-adequate group. Sperm quality was also affected, with a trend towards decreased total sperm motility observed in participants in the calorie surplus group after an ultra-processed diet.
Because ultra-processed foods are highly industrially processed and packaged, the researchers also tested participants for chemical contaminants. They found a trend toward higher levels of cxMINP, a compound related to phthalates (plasticizers), in the blood of participants after an ultra-processed diet. Additionally, ultra-processed diets were associated with lower blood levels of lithium, a mineral important for regulating mood, and there was a corresponding tendency for depression scores to increase in the calorie-adequate group.
“In conclusion, our results show that UPF intake itself is detrimental to human health, regardless of excess caloric intake,” the study authors wrote. “Shifting dietary patterns away from UPF and toward less processed alternatives may promote cardiometabolic and mental health, along with improved male fertility.”
This study makes a significant contribution to the scientific understanding of the health effects of consuming ultra-processed foods, proving that the negative effects go far beyond simply overeating. However, it should be noted that although the study authors provided meals to participants, information about their actual dietary adherence (and whether they ate out) was based on self-reporting, leaving room for reporting bias. Additionally, the duration of the diet was relatively short at three weeks, and the study only included healthy young men, so results may be different for women, older adults, or those with pre-existing obesity.
The paper, “Effects of Ultra-Processed Food Consumption on Male Reproductive and Metabolic Health,” was written by Jessica M. Preston, Joe Iversen, Antonia Hufnagel, Rein Hjort, Jodi Taylor, Clara Sanchez, Victoria George, Anne N. Hansen, Lars Anquist, Susan Herman, Jeffrey M. Craig, Signe Trekov, Christian Lind, and Karin. S. Fugard, Marcelo A. Nobrega, Stephen J. Simpson, Romain Valles.
