The bag of chips comes out, a child promises to have just a few, and twenty minutes later the bag is empty.
For many parents, it feels like something takes over the moment the snack lands on the table.
A new study suggests there is something to that feeling. Children who ate more ultra-processed foods showed noticeably stronger activity in the brain's reward center when they looked at tempting foods.
The research was published in late October 2026 in JAMA Network Open. The same brain response also helped predict which kids put on more weight over the following year.
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The study was led by researchers at USC's Keck School of Medicine. They followed 46 children between ages 7 and 10, all of them starting at a healthy weight.
Each child took part in a brain scan while being shown pictures of appetizing foods like cookies and fries.
The team also tracked what the children normally ate and measured their body size and body fat at the start and a year later.
Why the reward center keeps asking for more
The brain region that stood out is called the dorsal striatum. It is part of the reward and motivation system, the same circuit that nudges us to keep doing things that feel good.
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In the kids who ate more ultra-processed foods, this area lit up more strongly when the food pictures appeared.
The brain response was not just a snapshot. It helped explain what happened on the scale over the following year.
When the researchers factored in the dorsal striatum activity, the link between ultra-processed eating and body mass index shrank by 31 percent. The link to body fat shrank by 44 percent.
In plain terms, a big part of the weight gain tied to ultra-processed foods seemed to run through how strongly the brain reacted to the sight of food.
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Kathleen Page, the senior author, told USC's Keck School of Medicine that childhood is a sensitive window. "Children's brains are still developing, habits are still forming and food preferences are still being made," she said.
The study is small, with only 46 participants, and it is observational. It cannot prove that ultra-processed foods caused the stronger brain responses.
The pattern was consistent enough, though, that the authors believe the reward system is doing real work here.
What two-thirds of American kids' plates look like
The backdrop makes the finding hard to brush off. Ultra-processed foods now make up roughly two-thirds of the calories American children eat.
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A national analysis of more than 33,000 young people published in JAMA in 2021 put the figure at 67 percent, up from 61 percent two decades earlier.
Ultra-processed foods are not simply foods that come in a package. The term describes industrially made products built from refined ingredients, additives, flavorings and emulsifiers.
Think packaged breakfast cereals, chicken nuggets, sweetened yogurts, chips, soda and most ready-to-heat meals.
The USC team suggests that steady exposure during childhood may be teaching the brain to respond more intensely each time these foods appear.
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Over months and years, that stronger pull may make it harder for a child to stop at one serving.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.