A Virginia Tech study finds that ultra-processed diets may prompt 18- to 21-year-olds to eat more and snack when they are not hungry, while slightly older young adults do not show the same pattern. After two weeks on an ultra-processed diet, younger participants consumed more at a buffet meal and were more likely to keep eating despite reporting no hunger, suggesting a period of heightened vulnerability in late adolescence.
Rates of excess weight are climbing among young people in the United States. An analysis in The Lancet has projected that by 2050, about one in three Americans between 15 and 24 years old could be living with obesity, increasing their risk for serious health problems.
Many factors contribute to this trend, including genetics and low physical activity, but diet plays a central role. Ultra-processed foods currently account for an estimated 55% to 65% of daily calorie intake among U.S. young adults, and prior research has linked high consumption of these products to conditions such as metabolic syndrome and poor cardiovascular health in adolescents, according to Virginia Tech researchers and other studies.
To better understand how ultra-processed foods affect eating behavior in young people, researchers at Virginia Tech conducted a tightly controlled crossover feeding trial involving 27 men and women aged 18 to 25 whose weight had remained stable for at least six months. Each participant completed two separate two-week diet periods, with a four-week washout interval in between during which they returned to their usual eating habits.
In one diet period, 81% of total calories came from ultra-processed foods such as packaged snacks and ready-to-eat items. In the other period, no ultra-processed foods were included. The diets were designed to provide only the calories needed to maintain each participant’s weight.
Investigators carefully matched the two diets on 22 characteristics, including macronutrients, fiber, added sugar, energy density, and a range of vitamins and minerals, to isolate the impact of food processing itself. Breakfasts were served in the laboratory, and remaining meals were prepared in a metabolic kitchen.
After each two-week diet period, participants arrived at the lab in a fasting state and were offered an all-you-can-eat buffet-style breakfast. They received a tray containing roughly 1,800 calories of food — about four times the energy in a typical American breakfast — with both ultra-processed and minimally processed options, and had 30 minutes to eat as much or as little as they wished.
To assess eating in the absence of hunger, participants were then given a tray of snack foods immediately after the meal. For 15 minutes, they were asked to taste each item and rate its pleasantness and familiarity. After the initial tasting, they could either continue eating the snacks or stop.
When researchers analyzed the full group, the type of diet — ultra-processed or non-ultra-processed — did not change the total calories or grams of food consumed at the buffet, nor did it alter the proportion of ultra-processed foods selected. These results did not differ by sex or by body mass index, a standard measure of body fat.
However, age made a clear difference. Participants aged 18 to 21 consumed more calories at the buffet breakfast after the ultra-processed diet than after the non-ultra-processed diet. They were also more likely to keep eating from the snack tray even when they reported they were no longer hungry. In contrast, those aged 22 to 25 did not show these increases in intake after the ultra-processed diet.
“Although this was short-term trial, if this increase in caloric intake persists over time, this could lead to weight gain in these young people,” said Brenda Davy, a senior author on the paper and a professor in Virginia Tech’s Department of Human Nutrition, Foods, and Exercise.
“The younger age group took in more calories from ultra-processed foods, even when they weren’t hungry,” said neuroscientist and co-author Alex DiFeliceantonio, an assistant professor at Virginia Tech’s Fralin Biomedical Research Institute at VTC who studies the mechanisms of food choice. “Our adolescent participants had just consumed more in the buffet meal after the ultra-processed diet. Then, given the opportunity to snack when not hungry, they ate more yet again,” she added, noting that snacking when not hungry is an established predictor of later weight gain in young people.
The team used the NOVA classification system, developed by nutrition researchers at the University of São Paulo in Brazil, to categorize foods based on the extent and purpose of processing. Under NOVA, ultra-processed foods — including soft drinks, flavored yogurts, and many pre-packaged snacks and prepared meals — are distinguished from unprocessed or minimally processed items such as fruits, legumes, and plain yogurt.
Earlier trials in adults that provided continuous access to ultra-processed foods have shown that people tend to eat more overall and gain weight. In contrast, the Virginia Tech study matched daily calories and energy density between diets and measured intake at a single buffet meal, helping to isolate the role of processing itself in driving excess energy intake.
The findings, published in the journal Obesity and supported by grants from the U.S. National Institutes of Health, suggest that late adolescence and early adulthood may represent a particularly sensitive developmental window. As young people gain independence and establish their own eating patterns, high exposure to ultra-processed foods may increase their tendency to eat beyond hunger, potentially shaping their long-term weight and health trajectories.
