- In a small controlled feeding trial, 18 to 21 year olds ate more after two weeks on an ultra processed diet
- The older group, aged 22 to 25, did not show the same increase
- The biggest concern was extra snacking after a meal, because eating when not hungry is linked with later weight gain
A Virginia Tech study suggests late adolescence may be a particularly sensitive period when it comes to ultra processed foods.
After just two weeks on a diet high in ultra processed foods, participants aged 18 to 21 ate more at a buffet breakfast and were more likely to keep snacking afterwards, even when they were no longer hungry.
Participants aged 22 to 25 did not show the same pattern.
The researchers recruited 27 men and women aged 18 to 25 whose weight had been stable for at least six months.
Each person followed two different diets for two weeks each, with a four week break in between.
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One diet was built so that 81% of calories came from ultra processed foods.
The other contained no ultra processed foods.
Meals were carefully prepared and the two diets were closely matched across 22 characteristics, including macronutrients, fibre, added sugar, energy density and a range of vitamins and minerals.
The aim was to isolate food processing itself, rather than obvious differences like calories or sugar.
After each diet period, participants were invited to a buffet style breakfast and told to eat as much or as little as they wanted.
Immediately afterwards, they were given snacks as part of a taste rating task, then allowed to keep eating if they chose.
This second stage was used to measure eating in the absence of hunger.
When everyone was analysed together, the diet did not change total calories eaten at the buffet.
The age split changed the story. The younger group ate more after the ultra processed diet, then carried on eating more during the snack period.
The researchers highlight that eating without hunger is a known red flag for later weight gain, which is why they see this as more than a trivial finding.
The study also leans on the NOVA food classification system, which groups foods by how heavily they are processed.
Ultra processed foods in NOVA tend to be industrial formulations with additives and ingredients not commonly used in home cooking, such as many packaged snacks, ready meals and soft drinks.
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There are limits.
The trial was short, the sample size was small and the key outcome was what happened at one buffet meal rather than over weeks of real world eating.
Still, the tight diet matching is a strength, and the age difference is a signal worth following up with larger, longer studies, ideally including younger teenagers and more natural eating conditions.
Reference: Rego MLM et al. The Influence of Ultraprocessed Food Consumption on Energy Intake in Emerging Adulthood: A Controlled Feeding Trial. Obesity. 2025. DOI: 10.1002/oby.70086
