Department of Research & Evaluation News

Children who ate more ultraprocessed foods showed stronger activity in a part of the brain involved in reward, and that brain response was linked to greater gains in body fat over the following year, a new study found.

The study — published October 2026 in JAMA Network Open — followed 46 children ages 7 to 10 who were at a healthy weight when the study began. Researchers looked at whether regularly eating ultraprocessed foods was related to how the children’s brains responded to food cues, and whether those responses were linked to later changes in body fat.

“These findings give us a better understanding of a potential pathway linking ultraprocessed food consumption with changes in body fat during childhood,” said study co-senior author Anny H. Xiang, PhD, MS, a research scientist with the Kaiser Permanente Southern California Department of Research & Evaluation. “What is particularly interesting is that these children were at a healthy weight when the study began, suggesting that reward-related brain responses may be important to understanding how dietary patterns influence future growth and body composition.”

Studying diet and the brain

Ultraprocessed foods are generally industrially made products that can be high in calories, low in nutrients, and made to be especially appealing. On average, ultraprocessed foods make up 67.7% of U.S. children’s daily calories.

Previous research has linked eating more ultraprocessed foods with obesity-related outcomes but less is known about how the brain may play a role in those links among children. The study used data from the BrainChild study, which recruited children through Kaiser Permanente Southern California. Dr. Xiang is one of 2 principal investigators on that study.

At the start of the study, children completed dietary assessments and had their body composition measured. Researchers also used functional magnetic resonance imaging to measure brain activity while children viewed pictures of foods and nonfood objects. Body composition was measured again about a year later.

Stronger response to food cues

Children who got more of their calories from ultraprocessed foods showed greater activity in the dorsal striatum when viewing food images. This part of the brain plays a role in learning, motivation, reward, and the development of habits.

Greater activity in this brain region at the start of the study was linked to increases in both body mass index and body fat percentage over the following year. Higher ultraprocessed food intake was also linked to a greater increase in waist circumference.

The findings suggest that the brain’s reward response to food may be one reason eating more ultraprocessed foods is linked with later weight gain.

More research needed

The researchers caution that the study was observational, meaning it cannot show that eating ultraprocessed foods caused changes in children’s brains or increases in body fat. The study was also relatively small, with 46 participants, and brain activity was measured at only one point in time.

Still, the study adds to existing research by bringing together detailed information on diet, brain imaging, and changes in body fat over time in the same children. This is the first study, to the author’s knowledge, to suggest that the dorsal striatum’s response to food cues may be one pathway linking diets high in ultraprocessed foods with later increases in body fat among children who started at a healthy weight.

The authors said larger studies, including those that measure brain activity more than once and include children of different ages and weight groups, are needed to confirm the findings and better understand how these connections may change over time.

In addition to Dr. Xiang, authors of the study include lead author Jasmin M. Alves, PhD; Ella Morgan, BA; Brendan Angelo, MS; Kianna Le, BS; Jared Smith, MS; and co-senior author Kathleen A. Page, MD, all of the Keck School of Medicine, University of Southern California; Ting Chow, PhD, of the Department of Research & Evaluation; and Kay Jann, PhD, of the University of Southern California. Dr. Xiang is also affiliated with the Kaiser Permanente Bernard J. Tyson School of Medicine.