Ultra-Processed Foods Make Young Adults More Likely to Overeat Even When They’re Not Hungry

A new study from Virginia Tech is raising important questions about how ultra-processed foods affect the eating habits of young adults, especially late teens. The researchers set out with a straightforward goal: to understand whether a diet high in these foods changes how much people eat, even when they’ve already had enough. Their findings suggest that 18- to 21-year-olds may be especially vulnerable, showing a stronger tendency to overeat after being exposed to an ultra-processed diet compared with slightly older participants.

The concern comes at a time when rates of obesity among young Americans are climbing. A report in The Lancet predicts that by 2050, one in three Americans aged 15 to 24 will meet the medical criteria for obesity. Many factors play into this trend—from genetics to sedentary lifestyles—but diet remains one of the biggest contributors, and ultra-processed foods now make up 55% to 65% of what young adults in the U.S. eat.

Ultra-processed foods have already been linked to metabolic syndrome, poor cardiovascular health, and other issues in adolescents. What scientists have been trying to understand better is how these foods shape actual eating behavior in real time. This new Virginia Tech study offers some of the clearest laboratory evidence to date that age may play a key role.

Study Design and How It Worked

The researchers recruited 27 participants between ages 18 and 25, all of whom had maintained stable body weight for at least six months. Every participant went through two separate two-week diet periods:

• One diet where 81% of calories came from ultra-processed foods.
• Another diet with zero ultra-processed foods.

To keep things scientifically tight, each person served as their own control. After completing one two-week diet, they returned to their normal eating habits for four weeks, and then switched to the other diet.

Meals were carefully prepared in a metabolic kitchen, with breakfast eaten in the lab each day. The researchers went to great lengths to match both diets on 22 nutritional characteristics, including macronutrients, fiber, added sugars, energy density, and a wide list of vitamins and minerals. This level of diet matching is extremely rare in studies of this kind, and it allowed the team to isolate whether the processing of the food—rather than its nutritional content—affected eating behavior.

To classify the foods, the team relied on the NOVA system, developed by nutrition researchers in Brazil. Under NOVA:

• Unprocessed/minimally processed foods include items like fresh fruit, plain yogurt, and legumes.
• Processed culinary ingredients include oils, butter, and salt.
• Processed foods include canned vegetables, cheese, or freshly baked bread.
• Ultra-processed foods include soft drinks, flavored yogurt, pre-packaged meals, and most packaged snacks—essentially products altered through industrial processes and containing additives not typically used in home cooking.

Testing Eating Behavior

After each two-week diet phase, the participants arrived at the lab fasted and were served a buffet-style breakfast totaling about 1,800 calories—roughly four times the calorie load of a typical American breakfast. They had 30 minutes to eat as much or as little as they wanted.

Immediately afterward, participants completed an “eating in the absence of hunger” test. They received a tray of snacks, took one bite of each, rated them, and were then given 15 minutes to either eat more or simply relax. This test helps researchers understand whether people are eating purely for reward or habit—not for hunger.

What the Researchers Found

When looking at all participants as a single group, the study did not find an overall increase in calories consumed at the buffet after the ultra-processed diet. It also did not find any changes related to participants’ sex or BMI.

But when the team analyzed the results by age, a significant difference appeared:

• 18- to 21-year-olds ate more calories after spending two weeks on the ultra-processed diet.
• 22- to 25-year-olds did not show this change.

Younger participants also ate more during the non-hunger snacking session, indicating that the ultra-processed diet increased their likelihood of eating even when their bodies didn’t need food.

This finding is especially important because snacking without hunger is strongly linked to future weight gain in young people. The study suggests that exposure to highly processed foods may amplify this behavior during late adolescence, a period when long-term eating habits are being formed.

Why This Study Matters

Past clinical trials in adults have also shown that ultra-processed diets lead to increased daily calorie intake and weight gain. However, those studies did not control nutrients as tightly and allowed people continuous access to food. In those cases, higher calorie intake naturally led to weight gain, which then increased daily energy needs—making it hard to isolate the effect of food processing alone.

This new study kept participants weight-stable and controlled exact calorie provision, making it clearer that the processing of the food itself may influence appetite and overeating, especially in younger adults.

The researchers note the study’s limitations too:

• The short duration may not reflect long-term eating patterns.
• It assessed behavior at only one meal rather than continuous access to food.
• The small sample size means larger studies are needed to confirm the age differences.

Even with these limits, the findings support the idea that late adolescence may be a sensitive developmental window in which ultra-processed foods can have stronger behavioral effects.

Additional Background: What Makes Ultra-Processed Foods So Problematic?

Ultra-processed foods are everywhere—cheap, convenient, engineered to taste good, and aggressively marketed. But why are they so often linked to weight gain and overeating?

Here are some key reasons researchers point to:

Hyper-Palatability

UPFs combine high levels of sugar, salt, fat, and flavor additives designed to keep people eating. These combinations can override natural satiety cues.

Fast Consumption

Many UPFs require little chewing and can be eaten quickly. Faster eating is associated with greater calorie intake.

Weaker Satiety Signals

Because UPFs tend to be low in protein and fiber, they may not trigger the fullness response as effectively as whole foods.

Reward System Activation

Research suggests that UPFs may stimulate the brain’s dopamine-driven reward pathways more intensely than minimally processed foods. This makes them harder to resist, especially for young people whose reward systems are more active and still developing.

Constant Availability

In modern settings, UPFs are the default choice: vending machines, convenience stores, fast-food chains, campus dining halls, and packaged foods at home.

The new Virginia Tech study doesn’t claim to answer all these questions, but it adds important experimental evidence showing that even when all other nutritional factors are carefully controlled, ultra-processed foods may push younger adults to eat more.

Where the Research Is Headed Next

The team suggests several ways future studies could expand:

• Testing younger teens to see if susceptibility appears even earlier.
• Extending the diet periods beyond two weeks.
• Using continuous food access rather than single-meal tests.
• Incorporating neuroimaging or biomarker data to understand the biological mechanisms driving overeating.

Understanding these mechanisms could help develop interventions—or policy changes—to reduce obesity risk during crucial developmental stages.

Research Paper:
https://doi.org/10.1002/oby.70086