Young adults in their late teens and early twenties continued consuming excessive calories—even when not hungry—after spending just two weeks on a diet high in ultra-processed foods, according to new research.
The same pattern didn’t emerge among similarly aged individuals who had followed a two-week diet emphasizing healthier, unprocessed foods instead.
Much of the extra calorie consumption among those exposed to ultra-processed foods came from snacking between meals.
Study co-author Alex DiFeliceantonio, an assistant professor with the Fralin Biomedical Research Institute at Virginia Tech in Blacksburg, explained the significance: “Snacking when not hungry is an important predictor of later weight gain in young people, and it seems ultra-processed food exposure increases this tendency in adolescents.”
The Ultra-Processed Food Problem
Ultra-processed foods currently make up as much as 65% of daily calorie intake for Americans between ages 15 and 24, researchers noted.
These foods are manufactured primarily from substances extracted from whole foods, including saturated fats, starches, and added sugars. They also contain numerous additives designed to enhance taste, visual appeal, and shelf life. Common examples include packaged baked goods, sugary breakfast cereals, ready-to-eat or ready-to-heat meals, and deli meats.
In contrast, whole foods such as fruits, vegetables, and whole grains remain unprocessed, while many dairy products undergo only minimal processing.
Previous research has connected ultra-processed foods to metabolic syndrome, cardiovascular problems, and other health issues in younger populations, according to the research team.
Study Design
DiFeliceantonio’s team wanted to determine whether exposure to these foods might promote overeating more broadly. They enrolled 27 participants ages 18 to 25, assigning each to follow one of two diets for two weeks. The findings appeared on November 19 in the journal Obesity.
One diet derived 81% of its calories from ultra-processed foods, while the other contained zero calories from ultra-processed sources. Researchers carefully balanced both diets to match typical U.S. macro- and micronutrient profiles.
Senior author Brenda Davy, a professor of human nutrition, foods and exercise at Virginia Tech, emphasized the study’s rigor: “We very rigorously designed these diets to be matched on 22 characteristics, including macronutrients, fiber, added sugar, energy density and also many vitamins and minerals. Previous studies had not matched diets to this extent.”
Key Findings
After completing their two-week specialized diets, participants returned to normal eating patterns for a month while researchers monitored their habits. The team paid particular attention to how much participants consumed at an all-you-can-eat breakfast buffet and their use of post-breakfast snack trays.
Looking at the entire group of 27 participants, researchers initially saw no major differences in calorie intake or preference for ultra-processed foods after the diet period ended.
However, when they analyzed the data by age groups, a clear pattern emerged. The younger participants—those ages 18 to 21—consumed significantly more calories at buffet breakfasts if they had just completed the ultra-processed food diet.
These younger participants also snacked considerably more despite having just finished breakfast and reporting no hunger.
DiFeliceantonio, who also serves as an assistant professor in the Department of Human Nutrition, Foods, and Exercise, noted: “Given the opportunity to snack when not hungry, they ate more yet again.”
This increased consumption didn’t occur among 18-to-21-year-olds who had followed diets featuring unprocessed or minimally processed foods.
Implications and Future Research
Davy highlighted the potential long-term consequences: “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.”
The research team believes additional studies are needed, particularly involving larger groups of younger teenagers and conducted in more real-world environments.
Further investigation into the mechanisms behind food-triggered overeating—including studies examining brain activity and biological markers—would also prove valuable, the researchers suggested.
This study adds to mounting evidence that ultra-processed foods may affect eating behaviors in ways that extend beyond their immediate consumption, potentially contributing to long-term health challenges for younger populations.