The number of overweight young people in the United States is on the rise. An analysis published in The Lancet predicts that by 2050, about one in three Americans between the ages of 15 and 24 will meet the criteria for obesity, putting them at higher 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 – which make up 55 to 65 percent of the diets of young adults in the U.S. – have been linked to metabolic syndrome, poor cardiovascular health and other diseases in adolescents.
The situation in Europe regarding overweight and obesity among young people is also serious. According to OECD data from 2022, an average of 20% of 15-year-old adolescents in member countries – including many European countries – were overweight or obese. WHO and World Obesity Atlas projections suggest that the number of children and adolescents with obesity will increase significantly by 2035 – by around 60% for boys and 57% for girls across Europe.
Highly Processed Foods and the Susceptibility of Young People
Researchers at Virginia Tech investigated how a diet high ultra-processed foods affects young adults aged 18 to 25. They compared two types of diets: one high in highly processed foods and one without. After two weeks with each diet, they tested whether the participants ate differently when faced with an all-you-can-eat buffet.
When the researchers looked at all participants in the study together, they found no overall increase in calories or grams of food consumed at a breakfast buffet after the different diets. However, a different picture emerged when they focused on age. Participants between the ages of 18 and 21 consumed more calories at breakfast after eating ultra-processed foods, while 22 to 25-year-olds did not show this increase. The findings, to be published in the journal Obesity, suggest that adolescents and very young adults may be more susceptible to the effects of ultra-processed foods.
“Although this was a short-term study, this increase in caloric intake, if sustained over a longer period of time, could lead to weight gain in these young people,” said Brenda Davy, lead author of the study and a professor in Virginia Tech’s Department of Human Nutrition, Food and Exercise. “The younger age group consumed more calories from ultra-processed foods even when they weren’t hungry,” said neuroscientist and co-author Alex DiFeliceantonio, assistant professor at Virginia Tech’s Fralin Biomedical Research Institute, who studies the mechanisms of food choice. It is important to understand this age group because adolescence and young adulthood are important developmental stages. As independence increases, eating habits become more entrenched and the risk of obesity increases.
Controlled Eating in Young Adults
The team recruited 27 men and women between the ages of 18 and 25 whose weight had remained stable for at least six months. For two weeks, each participant followed one of two diet plans, which included a lab-served breakfast, while the remaining meals were prepared in a Metabolic Kitchen. In one diet, 81 percent of total calories came from ultra-processed foods. The other contained no highly processed foods at all.
The researchers carefully matched the nutritional content of the two diets. Participants were given only the amount of calories needed to maintain their weight, and the team measured how much they ate at a single buffet meal after each tightly controlled diet phase. “We matched these diets very strictly on 22 characteristics, including macronutrients, fiber, added sugars, energy density, and lots of vitamins and minerals,” Davy said. “Previous studies had not matched diets to this extent.”
How Foods Were Classified Using the NOVA System
The researchers used the NOVA classification system – “nova” means “new” in Portuguese – which groups foods according to their level of processing. Nutrition experts at the University of São Paulo in Brazil developed this system when they were investigating the rapid rise in obesity in their country.
Unprocessed or minimally processed foods include fresh fruit, pulses and natural yogurt, for example. Processed cooking ingredients such as cooking oils, butter and salt form another category. Processed foods – cheese, canned vegetables or freshly baked bread – combine these ingredients through relatively simple processes. Highly processed foods such as soft drinks, flavored yogurt and most pre-packaged meals and snacks are industrially produced and contain additives that are rarely used in home cooking. Each participant acted as their own comparison in this crossover study. They followed one of the diets for two weeks, then returned to their usual eating habits for four weeks and then switched to the other diet.
Breakfast Buffet and Eating Without Hunger
After each two-week diet phase, participants were invited to eat freely from the breakfast buffet, which included both ultra-processed and non-heavily processed options. They arrived in a fasted state and were escorted to a private room where they were given a tray containing about 1,800 calories – four times the calorie content of a typical American breakfast. They were given 30 minutes to eat as much or as little as they wanted.
To study eating without hunger, participants were given a tray of snacks immediately after breakfast. They were asked to take a bite of each snack for 15 minutes and rate how pleasant and familiar it was to them. Once they had tasted and rated all the products, they could choose to continue eating or simply rest for the rest of the session.
The Result: Younger Participants Ate More
Across the entire group of participants, the type of diet they had just followed had no effect on the total calories or the total amount of food they ate at the buffet. The proportion of ultra- processed foods selected also remained similar. These results did not differ by gender or body mass index (BMI), a standard measure of body fat.
However, the breakdown by age revealed an important difference. The 18- to 21-year-olds, but not the 22- to 25-year-olds, consumed more calories after the ultra-processed diet. The younger participants were also more likely to continue eating when they were no longer hungry.
“Our young participants had simply eaten more from the buffet after the ultra-processed diet. Then when they had the opportunity to snack even though they weren’t hungry, they ate even more,” said DiFeliceantonio, who is also an assistant professor in the Department of Human Nutrition, Food and Exercise. “Snacking despite not being hungry is an important predictor of later weight gain in young people, and it appears that consumption of ultra-processed foods exacerbates this tendency in adolescents.”
Isolating the Effects of Food Processing
Previous clinical studies of adults who were continuously offered ultra-processed foods found that people ate more each day and gained weight over time. In contrast, the Virginia Tech study kept daily calories and energy density the same between diets and assessed intake at a buffet-style meal.
“This is important because it helps isolate the impact of food processing on energy intake,” DiFeliceantonio said. “In the previous study, participants ate more each day, which meant they gained weight each day, which also increased their energy needs. Here, since all participants had a stable weight, we can look at the influence of processing alone.” The researchers point out that the short duration of the study and its focus on a single meal may not fully reflect how people deal with food in everyday life, where opportunities to eat are almost constant.
Future Research on Ultra-Processed Foods and Adolescents
Davy suggests that future research could extend the intervention period, include younger participants, or provide continuous access to food to better reflect real-world conditions. This study also included a modest number of participants, so repeating it with a larger group could provide a clearer picture of how age affects responses to highly processed diets.
By using tools such as brain imaging and biomarkers, scientists could potentially uncover the biological pathways that link consumption of ultra-processed foods to changes in eating behavior during development. This is an active area of research for DiFeliceantonio and Davy. This research was supported by a grant from the National Institutes of Health.