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Brenda Davy and Alex DiFeliceantonio working in the Fralin Biomedical Research Institute at Virginia Tech Carilion’s metabolic kitchen, where dietary and behavioral studies are conducted.

Credit: Clayton Metz/Virginia Tech

Obesity is on the rise among young Americans.

A recent study featured in The Lancet projects that by 2050, about one-third of individuals between 15 and 24 years old in the U.S. will be classified as obese, placing them at significant health risk.

Although various factors such as heredity and physical inactivity play a role, dietary habits are a major contributor.

Ultra-processed foods — which comprise 55 to 65 percent of what young adults in the U.S. consume — have been linked to poor heart health, metabolic disorders, and other health challenges in adolescents.

Scientists at Virginia Tech set out to explore the impact of diets rich in ultra-processed foods versus those without them in individuals aged 18 to 25. Specifically, they examined how each diet might influence eating behavior during a buffet meal after a two-week period.

In a controlled trial, researchers found that while the overall food intake at a post-diet buffet meal didn’t change significantly, individuals aged 18 to 21 consumed more calories after being on an ultra-processed diet. This pattern wasn't observed in participants aged 22 to 25. The findings, to be published on November 19 in the journal Obesity, suggest younger participants are especially sensitive to these food types.

“Even though this was a short-term study, if this increased calorie consumption continues over time, it could eventually promote weight gain in these younger individuals,” said Brenda Davy, senior study author and a professor in the Department of Human Nutrition, Foods, and Exercise at Virginia Tech.

“We found that the younger individuals ate more ultra-processed foods, even when they weren’t hungry,” added neuroscientist and co-author Alex DiFeliceantonio, an assistant professor at the Fralin Biomedical Research Institute who studies food-related behaviors.

This age group is important to study, as adolescence and early adulthood mark a time when lifelong habits are formed and the risk of obesity begins to rise.

How the Study Was Conducted

Twenty-seven men and women ages 18 to 25, whose weight had been stable for at least six months, were selected for the study. For two weeks, each participant followed one of two specific meal plans: one where 81 percent of the calories came from ultra-processed foods and one without any ultra-processed food. Meals were carefully prepared in a lab setting, with breakfast served in the lab and other meals crafted in a controlled kitchen environment.

Each meal plan was nutritionally equivalent, constructed to match in 22 specific categories such as macronutrients, added sugars, fiber, vitamins, and energy density, with the aim of isolating the effects of food processing itself, Davy explained. Few previous studies have matched diets so precisely.

The teams used the NOVA system — a food classification method developed at the University of São Paulo that organizes foods by processing level. Under this system, unprocessed items include fresh fruits and plain yogurt, while ultra-processed items, like soft drinks and packaged snacks, are made through industrial methods and often contain additives rare in home cooking.

Participants acted as their own controls through a crossover design: after completing one diet for two weeks, they returned to their usual eating habits for four weeks, then switched to the opposite diet.

After each two-week phase, participants were offered a buffet-style breakfast where they could eat freely. They arrived after fasting and were served a tray containing about 1,800 calories’ worth of food — roughly four times the energy in a typical American breakfast. They had 30 minutes to eat as much or as little as they desired.

To assess how much they might continue eating without physical hunger, participants were then given extra snacks. After sampling and rating each snack based on enjoyment and familiarity, they had another 15 minutes to either keep eating or rest quietly.

Key Results

Looking at participants as a whole, the specific diet followed did not alter the total calories or food weight consumed at the buffet. Their selection of ultra-processed items also didn’t change significantly, regardless of factors like sex or BMI.

However, age made a difference. Young adults aged 18 to 21 ate more after the ultra-processed food diet, both at the large meal and when not particularly hungry during the snack period. This trend did not appear in the slightly older group.

"When the younger participants had access to the buffet following the ultra-processed diet, they ate more," said DiFeliceantonio, who also teaches in the Department of Human Nutrition, Foods, and Exercise. "They even went on to consume more snacks afterward, despite not feeling hungry. These behaviors are closely linked to future weight gain in adolescents."

Unlike prior studies that let people eat ultra-processed food freely and saw overall calorie counts rise, this study equalized calorie intakes and compared results in a single buffet-setting to better understand the isolated impact of food processing.

"That’s what makes our findings valuable," said DiFeliceantonio. "Since the participants didn’t gain weight during the study, we were able to focus purely on how food processing itself might influence behavior."

Though informative, the study's short time frame and its controlled design may not fully reflect real-world eating patterns, where food is constantly available.

Davy noted that future research could extend the duration, study younger individuals, or allow greater access to food to better simulate daily life. A broader pool of participants could also offer more insight into age-related trends.

Additionally, combining imaging and biological monitoring might reveal how exposure to highly processed foods affects the brain and decision-making around eating — a topic that DiFeliceantonio and Davy continue to explore.

This research received funding from the National Institutes of Health.

Journal

Obesity

DOI

10.1002/oby.70086

Method of Research

Experimental study

Subject of Research

People

Article Publication Date

19-Nov-2025