Children who get more of their calories from ultra-processed foods show stronger activity in a brain reward region when they look at pictures of tempting foods, and those stronger responses tracked with larger gains in body fat over the following year, according to a study from the Keck School of Medicine of USC.

The research, published in JAMA Network Open, involved just 46 children and was observational. It cannot show that ultra-processed food causes changes in the brain or causes weight gain, and the authors say a feeding trial is the next step.

Still, the findings point to a possible biological pathway linking the modern food environment to childhood weight gain, at a time when these products dominate what American children eat.

What the Brain Scans Showed

The study followed children ages 7 to 10 enrolled in USC's ongoing BrainChild study, which examines factors that contribute to diabetes and obesity. All had a healthy weight at the start.

Researchers measured each child's usual intake of ultra-processed foods through dietary assessments. They then used MRI scans while the children viewed pictures of appealing foods such as cookies and French fries, focusing on the dorsal striatum, a region involved in reward, motivation and habit formation. Body mass index, body fat percentage and waist circumference were measured at the start and again one year later.

According to ScienceDaily, children who ate more ultra-processed food showed greater dorsal striatum activity in response to the food images. Stronger responses were in turn linked to larger increases in BMI and body fat over the following year.

When researchers statistically accounted for those brain responses, the link between ultra-processed food and BMI weakened by 31 percent, and the link with body fat percentage weakened by 44 percent. That pattern suggests the brain's reward response may help explain part of the connection. A related region, the ventral striatum, did not show a statistically significant association, according to the published abstract summarized by Neuroscience News.

Putting the 67 Percent Figure in Context

Coverage of the study notes that ultra-processed foods make up about 67 percent of calories eaten by U.S. children. That figure does not come from the USC study. It comes from a 2021 JAMA analysis of federal survey data led by Tufts University, which found that the share rose from about 61 percent in 1999 to 67 percent in 2018 among youths ages 2 to 19, as summarized by the National Institutes of Health.

The trend is a product of the food system as much as individual choice. Ready-to-heat meals, packaged snacks and sweetened products are widely available, shelf-stable and relatively inexpensive, which is part of why they are so common in children's diets across income levels.

Senior author Dr. Kathleen A. Page, a professor of medicine and pediatrics at Keck, emphasized why the age group matters, saying "habits are still forming and food preferences are still being made."

The Evidence Check: Strong Signal, Small Study

This is an observational study of 46 children followed for one year. It shows an association, not cause and effect. The researchers cannot tell whether eating ultra-processed food changes how the brain responds, whether children with stronger reward responses are drawn to these foods in the first place, or whether other factors drive both.

The sample was also small and drawn from one Southern California cohort, so the results may not apply to all children. Ultra-processed foods were measured through dietary assessments, which rely on reported intake. And the term "ultra-processed" itself covers a wide range of products, from sugary drinks to some whole-grain breads, which some nutrition scientists argue makes the category too broad.

The study was funded by the American Diabetes Association and the National Institutes of Health.

Other research supports part of the picture. Controlled feeding trials in adults have found that ultra-processed diets can lead people to eat more and gain more weight than minimally processed diets, but those trials did not measure children's brain responses. The USC work adds a possible mechanism — not a verdict.

The Food Environment and What Families Can Do

Page has argued that improving children's diets cannot rest on families alone. "Changing the food environment to help people access healthier, more minimally processed foods" is an important part of the solution, she said in a USC statement reported by HealthDay.

That framing matters for policy debates over school meals, food marketing to children and access to fresh produce in neighborhoods with few grocery stores. For households, the findings do not change official nutrition guidance, and there is no need to eliminate every packaged food. Pediatricians generally recommend building meals around fruits, vegetables, whole grains, beans and minimally processed proteins, and swapping some packaged snacks for whole-food options where cost and time allow.

Practical steps can be small. Keeping cut fruit or vegetables visible at home, cooking simple meals in batches on weekends, and reading ingredient lists for long strings of additives are all reasonable starting points — none of them requires a complete overhaul.

Parents with concerns about a child's weight or eating habits should talk with their pediatrician rather than making drastic changes on their own.

What Comes Next

Page hopes to run an intervention study in which children who regularly eat ultra-processed foods are given more minimally processed alternatives. Researchers would then track whether their brain responses to food images change and whether those changes are tied to less weight gain. That kind of trial could test cause and effect directly. The BrainChild study will also continue following participants through puberty and into early adulthood.

What Readers Want to Know

What did the USC study find? Children who ate more ultra-processed food had stronger dorsal striatum responses to food images, and stronger responses were linked to greater increases in BMI and body fat a year later.

Does this prove ultra-processed food causes weight gain in kids? No. The study was observational and involved 46 children, so it shows an association, not cause and effect.

Where does the 67 percent figure come from? From a 2021 Tufts-led analysis in JAMA, which found ultra-processed foods made up 67 percent of calories eaten by U.S. youths ages 2 to 19 in 2018.

What is the dorsal striatum? A brain region involved in reward, motivation, and habit formation.

What happens next in the research? The lead researcher hopes to run an intervention trial providing minimally processed foods to test whether brain responses and weight gain change.

Should parents remove all processed food? The study does not change nutrition guidance. Parents with concerns should consult their pediatrician.