The brain’s reward signal weakened in teens
For years, scientists have linked ultraprocessed foods to obesity and diabetes. But this study looks deeper — into the brain. It asked a simple question: Does eating only ultraprocessed food change how the brain reacts to a treat like a milkshake?
The answer, for teens, appears to be yes.
Researchers studied 18- to 25-year-olds on two different diets for two weeks each. One diet was full of ultraprocessed foods. The other had zero ultraprocessed items — just whole grains, fresh meat, fruits, and vegetables. The meals were matched for calories, sugar, fat, and fiber, so the only real difference was how processed they were.
After each diet, participants drank a milkshake while in a brain scanner. Scientists watched how the orbitofrontal cortex — a part of the brain that helps us feel reward and satisfaction — responded.
In young adults aged 22 to 25, there was little change. But in those aged 18 to 21, the brain’s response dropped after the ultraprocessed diet. It actually increased after the unprocessed diet.
That means teens’ brains became less excited by food rewards — even tasty ones — after just two weeks of eating processed foods.
A dimmer switch for pleasure
Think of the brain’s reward system like a light dimmer. When you eat something delicious, the switch turns up. You feel good. That signal helps your body know when to stop eating.
But in teens on the ultraprocessed diet, the dimmer was turned down. Their brains didn’t light up as much.
This could explain why some teens keep eating even when they’re full. If food doesn’t trigger satisfaction, they may eat more to try to feel it.
It’s not about laziness or lack of control. It may be biology.
Teens’ brains are still under construction
Why did only younger participants show this change? The brain keeps developing into the mid-20s. The orbitofrontal cortex, which helps with decision-making and reward, is one of the last areas to mature.
That might make teens more sensitive to diet changes. Their brains may be more flexible — or more vulnerable.
The study also found something surprising. The more ultraprocessed food a person usually ate, the stronger their brain’s response to the milkshake — no matter which diet they were on.
That suggests long-term eating habits may rewire how the brain reacts to food. It could create a cycle: more processed food leads to less satisfaction, which leads to eating more.
But there’s a catch.
This doesn’t mean this treatment is available yet.
The study was small and short. It only lasted two weeks per diet. It also didn’t measure real-world eating behavior — just brain activity.
Researchers didn’t see weight changes or mood effects. And the findings only applied to a narrow age group. Young adults aged 22 to 25 showed no brain changes.
Still, the results add to growing concern about ultraprocessed foods. They’re not just empty calories. They may affect how the brain works — especially during key developmental years.
Experts say this kind of research helps explain why obesity is so hard to reverse. If food stops making the brain feel rewarded, people may keep eating to chase that feeling.
For families, the message isn’t about perfection. It’s about balance. Swapping one packaged meal for a home-cooked one may help. Choosing water over soda. Adding fruit instead of cookies.
These small shifts may support not just physical health, but brain health too.
The study was not designed to test long-term effects. It also used functional MRI, which shows brain activity but not behavior. So we can’t say for sure that these brain changes lead to overeating.
But the clues are strong.
What happens next? Larger, longer studies are needed. Researchers want to know if these brain changes last. Can the brain bounce back after switching diets? And do these effects lead to real-world problems like weight gain or disordered eating?
For now, the best advice is simple.
If you’re a parent, caregiver, or young adult, pay attention to food choices. Not just for the body — but for the brain.
The science is still unfolding. But one thing is clear: what teens eat today may shape how their brains respond tomorrow.
