A diet based on ultra-processed foods impairs metabolic and reproductive health, study finds

An experimental study looking into the health effects of a 3-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 adverse effects of the ultra-processed food diet were independent of total caloric intake. The paper was published in Cell Metabolism.

Ultra-processed foods are industrial formulations made mostly from refined ingredients and additives rather than whole foods. In the NOVA food classification system, they are the most heavily processed category of foods.

Ultra-processed foods typically contain substances such as refined sugars, hydrogenated oils, starches, and protein isolates. They also include additives like preservatives, flavor enhancers, artificial colors, and emulsifiers designed to improve taste and shelf life. Common examples are packaged snacks, sugary drinks, instant noodles, processed meats, and ready-to-eat meals.

Ultra-processed foods are usually convenient, highly palatable, and aggressively marketed. They tend to have high energy density and low nutritional quality, with limited fiber, vitamins, and minerals. Studies report that individuals consuming high amounts of these foods are at an increased risk of obesity, cardiovascular disease, and metabolic disorders. Some authors even propose that a diet based on ultra-processed foods can lead to a health condition referred to as food addiction.

Study author Jessica M. Preston and her colleagues wanted to compare the effects of an ultra-processed food diet with an unprocessed food diet on metabolic and male reproductive health. They conducted an experimental crossover study in which 43 healthy young men (aged 20 to 35) followed prescribed diets.

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All participants followed each of the two diets for a period of 3 weeks. One group started with the ultra-processed diet and then switched to the unprocessed diet, while the other group started with the unprocessed diet and switched to the ultra-processed diet. Study authors included a 12-week washout period between the two diets to allow any residual effects to dissipate before the participants started their second diet.

To isolate the effects of calories versus food quality, half of the participants received diets with an adequate number of calories to maintain their weight, while the other half consumed diets with an excessive number of calories (an extra 500 calories per day).

The two diets were strictly matched to have similar amounts of carbohydrates, proteins, and fats. However, the ultra-processed food diet was designed to reflect a typical Western diet. Compared to the unprocessed diet, it contained elevated levels of saturated fats, cholesterol, refined grains, added sugars, and dairy products, and lower amounts of fiber. In the ultra-processed diet, 77% of calories were derived from ultra-processed foods, while this was under 1% in the unprocessed food diet. Study authors supplied all food to the participants during the study periods.

Study participants visited the center 7 times: once for an eligibility assessment, twice before starting the diets, twice after the diets, and twice during the washout period. During each pre- and post-diet visit, participants completed surveys, underwent body and vital sign measurements, completed dual-energy X-ray absorptiometry (DXA) scans, and provided blood and semen samples.

Results showed that even when calories were strictly controlled, participants weighed 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 they accumulated approximately 1 kg more fat mass after the ultra-processed food diet.

The ultra-processed food diet also triggered adverse changes in metabolic health indicators. Total cholesterol was higher, and the ratio of low-density lipoprotein (LDL) to high-density lipoprotein (HDL) increased, though this was primarily seen in the adequate calorie group. In the excessive calorie group, the ultra-processed food diet was linked to increased diastolic blood pressure.

Crucially, the diet also negatively impacted male reproductive health. The ultra-processed food diet was followed by a decrease in follicle-stimulating hormone (FSH) levels in the excess calorie group, and a trend toward decreased circulating testosterone in the adequate calorie group. Sperm quality was also affected, with a trend toward decreased total sperm motility observed in participants in the excess calorie group after the ultra-processed diet.

Because ultra-processed foods are heavily industrially processed and packaged, the researchers also tested participants for chemical pollutants. They found a trend of higher levels of cxMINP, a chemical compound linked to phthalates (plasticizers), in the participants’ blood after the ultra-processed diet. Additionally, the ultra-processed diet was associated with lower levels of lithium in the blood—a mineral important for mood regulation—and a corresponding trend toward increased depression scores in the adequate calorie group.

“In conclusion, our results demonstrate that consumption of UPF itself, irrespective of excess caloric intake, is detrimental to human health,” the study authors wrote. “Moving dietary patterns away from UPF and toward less-processed alternatives may promote cardiometabolic and mental health, along with amelioration of male reproductive fitness.”

The study contributes heavily to the scientific understanding of the health effects of ultra-processed food consumption, proving that the negative impacts go far beyond simple overeating. However, it should be noted that while the study authors provided food for participants, information about their actual adherence to the diets (and whether they ate outside food) was based on self-reporting, leaving room for reporting bias. Additionally, the 3-week duration of the diets was relatively short, and the study only examined healthy, young men, meaning the results may differ for women, older adults, or individuals with pre-existing obesity.

The paper, “Effect of ultra-processed food consumption on male reproductive and metabolic health,” was authored by 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.