Kids who eat more ultra-processed food showed brain responses that predicted weight gain

Kathleen A. Page, a professor of medicine and pediatrics at the Keck School of Medicine of USC, and her colleagues scanned the brains of 46 children aged 7 to 10 and found that those who ate more ultra-processed food reacted more strongly to pictures of appealing foods. The children who reacted most gained more body fat over the next year. The results appeared in JAMA Network Open, and they point to the brain’s reward circuitry as one route from diet to weight. All 46 children started at a healthy weight, which makes the one-year changes harder to explain away.

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Dorsal striatum activity while viewing cookies and French fries

The paper, Ultraprocessed Food Intake, Striatal Response to Food Cues, and Adiposity Gain in Children, drew on the BrainChild study of diabetes and obesity risk. At baseline, each child lay in an MRI scanner while viewing photos of highly appetizing foods such as cookies and French fries. Researchers also recorded diet, body mass index, body fat percentage and waist circumference, then repeated the body measurements after one year.

Children with higher intake of ultra-processed food showed greater activity in the dorsal striatum, a region involved in reward and motivation. Stronger responses there were linked to larger gains in BMI and body fat percentage a year later, and children with higher intake had bigger waists, BMI and body fat at the end.

31% and 44% of the link runs through the striatum

The statistical test was a mediation analysis. When the researchers accounted for dorsal striatum response, the association between ultra-processed food intake and BMI weakened by 31%, and the association with body fat percentage weakened by 44%. In the team’s reading, brain reward responses may partly explain the link between the food and the weight, though a large share of it is left to other causes.

The Keck School of Medicine release quotes Page saying the study goes beyond understanding that these foods affect weight, and gives insight into the neurobiological underpinnings. She also noted that children’s brains are still developing, habits are still forming and food preferences are still being made, and said intervening early could make a real difference.

The numbers cut both ways. If accounting for striatal response weakens the diet-to-BMI link by 31%, about 69% of that link remains unexplained by the brain measure, and for body fat the remaining share is 56%. The brain response is a partial pathway in this sample. Because every child began at a healthy weight, the reward response was measured before any excess weight had appeared, which is why the team treats it as a candidate mechanism and not a result of weight already gained.

First author Jasmin M. Alves worked with Ella Morgan, Brendan Angelo, Kianna Le, Jared Smith, Kay Jann of the USC Stevens Neuroimaging and Informatics Institute, and Ting Chow and Anny H. Xiang of Kaiser Permanente Southern California.

The 67% of calories and the limits of 46 children

Ultra-processed products supply about 67% of the calories U.S. children eat, according to the ScienceDaily report of the study, so the range of intake within any group of children is narrower than the national average suggests. Obesity is already common at these ages: the Centers for Disease Control and Prevention puts prevalence at 20.7% among children 6 to 11 and about 1 in 5 across ages 2 to 19.

The cost side is documented too. CDC reports obesity at 12.7% among children 2 to 5 and 22.2% among adolescents 12 to 19, and estimates that children with obesity cost the U.S. health care system about $1.3 billion a year, roughly $116 more per child per year than children at a healthy weight.

The study is observational. It cannot show that ultra-processed food causes the brain response or the weight gain, and 46 children is a small sample. A News-Medical summary of the paper notes that the national calorie share is not a measurement from the study group, and the published summaries do not say which dietary method or classification system sorted foods into the ultra-processed category.

Page also said part of the solution is changing the food environment to help people access healthier, more minimally processed foods. The researchers acknowledge that ultra-processed products are often cheap, widely available and convenient, so what a family eats depends partly on what is on the shelf. The paper is listed as JAMA Network Open 2026;9(10):e2640252, and the USC release is credited to Zara Abrams.

The team has two follow-ups planned. BrainChild will keep tracking the same children through puberty and into early adulthood. Page also plans an intervention trial in which children who regularly eat ultra-processed food are given more minimally processed alternatives, to test whether the swap changes both the brain response and weight gain. Funding for the work came from the American Diabetes Association and the National Institute of Diabetes and Digestive and Kidney Diseases at NIH. The grant list is specific. The work drew on an American Diabetes Association Pathway Accelerator Award and two NIDDK awards, R01DK116858 and R01DK134079, with database support from the Southern California Clinical and Translational Science Institute.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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