Ultraprocessed foods make up more than half of what many young Americans eat. A new controlled study from Virginia Tech suggests that this heavy exposure may influence how older teens respond to food, even when their bodies aren’t asking for it.
The research, published in Obesity, tested how two different diets affected eating behavior among adults ages 18 to 25. For two weeks, participants followed either a diet where 81% of calories came from ultraprocessed foods or a diet with no ultraprocessed foods at all. Each participant completed both diets, separated by a four-week break.
The meals were tightly controlled. Breakfast was eaten in the lab, and the rest of the food came from a metabolic kitchen. Researchers matched the two diets as closely as possible, including calories, macronutrients, fiber, added sugar, energy density, vitamins and minerals, to isolate the effect of processing itself.
After each two-week period, participants were brought into a private room and offered a buffet-style breakfast containing roughly four times the calories of a typical morning meal. They were told to eat as much or as little as they liked. Afterwards, they were given a selection of snacks and invited to taste them, rate them and choose whether to continue eating, a way to measure “eating in the absence of hunger.”
Across all participants, the overall amount eaten at the buffet did not differ between diets. But a clearer pattern emerged when the researchers looked at age groups separately. Adults ages 22 to 25 showed no change in how much they ate. But those ages 18 to 21 consumed more calories after the ultraprocessed diet. They also ate more when they were no longer hungry.
“The younger age group took in more calories from ultraprocessed foods, even when they weren’t hungry,” said neuroscientist Alex DiFeliceantonio, an assistant professor at the Fralin Biomedical Research Institute at VTC. “Snacking when not hungry is an important predictor of later weight gain in young people, and it seems ultraprocessed food exposure increases this tendency in adolescents.”
This matters because late adolescence and early adulthood are a key developmental window. As teens leave home and make independent food choices, lifelong habits begin to form. It’s also a period when obesity risk starts to rise. A recent analysis in The Lancet predicts that one in three Americans age 15 to 24 will meet criteria for obesity by 2050.
Although the study used the NOVA classification system to categorize foods as ultraprocessed, the researchers emphasized that processing itself isn’t inherently negative. Many foods considered “ultraprocessed” in research, such as flavored yogurt, whole-grain breakfast cereals or packaged breads, can still contribute important nutrients. NOVA is based on the degree of industrial processing, not the nutritional value of a food, and different foods in this category can have very different health effects.
For nutrition scientists, the concern is less about processing as a concept and more about how certain UPFs are engineered. Many industrially produced snacks and ready-to-eat items combine refined starches, added fats, sugars and flavorings in ways that make them easy to overeat. Studies suggest these foods may be less satiating, more reinforcing and more likely to be consumed quickly, factors that can influence appetite regulation and eating behavior in some people.
This new study supports that perspective. The younger adults didn’t gain weight, and the meals were matched so closely that calories, nutrients and energy density were identical across diets. The change wasn’t metabolic, it was behavioral. After two weeks of eating mostly ultraprocessed foods, the 18- to 21-year-olds were more likely to keep eating even when they weren’t hungry, especially in a setting with plenty of tempting choices.
This doesn’t mean ultraprocessed foods are always harmful or that they need to be completely avoided. Instead, the findings suggest that certain products in this category may influence appetite differently during late adolescence, a time when food habits, and future health trajectories, are taking shape.
Although short in duration, this study helps untangle whether ultraprocessed foods change eating behavior on their own, separate from the effects of overeating or weight gain.
“This is important, because it helps isolate the effect of food processing on energy intake,” DiFeliceantonio said.
The researchers note that real life is far less controlled than a metabolic kitchen. People have continuous access to food, far more choices and more cues to eat. Future work could extend the intervention period, examine younger adolescents or incorporate brain imaging to explore why ultraprocessed food exposure may influence eating in this developmental stage.
For now, the findings suggest that food processing, not just calories or nutrients. may play a role in how some young adults respond to food, especially those still in the tail end of adolescence.
This research was funded by the National Institutes of Health.