If you have a teen at home—or at least remember being one—you’ve probably seen it firsthand. Given the choice, many kids and teens reach for nuggets, hot dogs, chips, or packaged snacks, even when there’s a home-cooked meal on the table.

A new study suggests that this preference may do more than shape taste. For older teens, regularly eating ultra-processed foods may make them more likely to eat more later—even when they’re no longer hungry.

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To better understand how these foods affect eating behavior, researchers looked beyond nutrition labels and focused on how processed foods shape appetite and eating patterns.

Participants completed two two-week diet phases in a crossover design, meaning each person followed both diets and served as their own control. One diet was high in ultra-processed foods, with 81% of calories coming from UPFs; the other contained none.

The diets were carefully matched for calories, macronutrients, fiber, energy density, and vitamins and minerals, allowing researchers to isolate the effects of food processing itself rather than differences in sugar, fat, or overall nutrition.

Meals were prepared at multiple calorie levels and adjusted as needed to keep participants weight-stable, preventing under- or overfeeding from influencing hunger and eating behavior.

After each diet phase, participants arrived fasting and ate freely from a breakfast buffet that included both ultra-processed and non-ultra-processed foods. They had 30 minutes to eat as much or as little as they wanted, while researchers measured intake, food choices, and eating rate.

Participants then completed a short snack session designed to measure eating in the absence of hunger. After tasting and rating each snack, they could continue eating or simply rest, even though most reported feeling full.

When researchers looked at everyone ages 18 to 25 together, the type of diet didn’t affect how much participants ate at the buffet. The diets also didn’t make people choose more ultra-processed foods overall.

But age made a clear difference. Participants ages 18 to 21 consumed more calories after the ultra-processed diet than after the non-UPF diet. They were also more likely to keep eating during the snack session, despite reporting low hunger and high fullness. In contrast, participants ages 22 to 25 did not show this pattern.

In other words, the younger group wasn’t eating more because they were hungrier. They were eating more despite not being hungry.

Adults aren’t off the hook. Ultra-processed foods make up roughly 50 to 60% of the average American’s diet, and a large body of research links high UPF intake in adults to increased risks of conditions such as type 2 diabetes, hypertension, and heart disease.

And their impact on appetite isn’t limited to teens. Studies show that UPFs make you eat more—and eat faster. Eating UPFs can also be hard to stop. The fast absorption of high amounts of fat and sugar triggers the brain’s reward system. No wonder some even argue that it meets the criteria for addiction used in tobacco.

This study doesn’t suggest that eating a processed snack once in a while is harmful or that teens or adults should avoid fast food altogether.

What it does suggest is that repeated exposure to ultra-processed foods may shape how teens eat later, making them more likely to consume extra calories even when hunger isn’t the driver.

Food choices don’t just matter now. Over time, they can influence appetite regulation, habits, and self-control, especially during developmental periods like adolescence. That’s why small, realistic changes can add up.

Cooking more meals from simple, minimally processed ingredients, keeping ultra-processed snacks and sugary drinks from becoming everyday defaults, and making whole foods the familiar, easy option at home can help support healthier eating patterns—now and into adulthood.

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