Ultra-Processed Foods Tied to Brain Reward Response and Fat Gain in Children, USC Study Finds
10 November 2026, Los Angeles, US: Children who get more of their calories from ultra-processed foods show a stronger response to food images in a brain region tied to habit and reward. That response predicted greater gains in body fat over the following year, according to researchers at the Keck School of Medicine of the University of Southern California (USC). The findings were published on October 23 in the peer-reviewed journal JAMA Network Open. They come from a small observational study and do not prove that the foods caused the changes.
The team followed 46 children aged 7 to 10, all at a healthy weight when they enrolled, as part of a long-running project known as the BrainChild study. Each child had a functional magnetic resonance imaging (fMRI) scan while viewing pictures of appetizing foods. fMRI tracks changes in blood flow as a proxy for brain activity. Researchers measured body mass index (BMI), body fat percentage and waist size again one year later.
Ultra-processed foods are industrially formulated products made largely from refined ingredients such as starches, oils, sugars and protein isolates, often with added flavorings, colors and emulsifiers. Examples include many packaged snacks, sweetened cereals, soft drinks and ready meals. Researchers classified the children’s diets using the widely used NOVA system, which groups foods by their degree of processing rather than by nutrient content.
Ultra-processed products made up a large share of what the children ate. On average they supplied 67.7% of daily calories in the group, whose mean age was 8.7 years and which was 57% female.
Children who ate more ultra-processed food showed a stronger response in the dorsal striatum, a region deep in the brain involved in forming habits and in learning to link cues with rewards. The association held after the researchers adjusted for other factors. A neighboring area, the ventral striatum, which is more closely associated with pleasure and motivation, did not show a statistically significant link.
A stronger dorsal striatum response at the start of the study, in turn, predicted larger increases in both BMI and body fat percentage over the next 12 months. Higher ultra-processed food intake was also associated with a larger increase in waist circumference across the year.
What the brain signal may explain
The researchers tested how much of the link between diet and weight gain could run through the brain response. When they accounted for dorsal striatum activity, the association between ultra-processed food intake and BMI gain weakened by 31%. The association with body fat gain weakened by 44%. That pattern suggests heightened sensitivity to food cues may be one route through which these diets relate to weight gain in children, though the design cannot confirm it.
The study’s senior and corresponding author is Kathleen A. Page, a professor of medicine and pediatrics and co-chief of the Division of Endocrinology and Diabetes at the Keck School of Medicine. The first author is Jasmin M. Alves. Collaborators included Kaiser Permanente Southern California and USC’s Stevens Neuroimaging and Informatics Institute.
Both the paper and USC’s own announcement stress the study’s limits. It is observational, meaning it identifies associations rather than cause and effect. The sample of 46 children is small, and follow-up lasted only one year, too short to show whether the patterns persist into adolescence.
The work was funded by an American Diabetes Association Pathway Accelerator Award and by grants from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the US National Institutes of Health (NIH). The NIH also provided support for data management.
Pressure on the processed food supply
The findings add to a growing scientific and policy debate over ultra-processed foods. Most of these products are built on a small set of commodity crops, chiefly corn, wheat, soybeans and sugar crops. These are processed into flours, syrups, starches and refined oils before formulation.
Researchers in the field have long debated where the harm attributed to ultra-processed foods comes from. One view points to their typical nutrient profile: high in added sugar, refined starch, salt and fat, and low in fiber. The other points to processing itself, including texture, additives and how quickly the foods can be eaten. The USC study does not settle that question. It does point to a possible behavioral mechanism: the dorsal striatum, a habit-forming region, responds more strongly to food cues in children who eat more of these products, at an age when the brain is still developing.
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