Show a child a picture of a warm cookie and something lights up in their brain. A new study from the University of Southern California suggests that this little spark may be brighter in kids who eat a lot of ultra-processed food, and that it could help explain why some of them gain weight.
What the researchers did
The team at the Keck School of Medicine of USC followed 46 children aged seven to ten, all of them at a healthy weight when the study began. They came from the BrainChild study, a long-running project on diabetes and obesity risk. Each child lay in an MRI scanner and looked at photos of tempting foods, such as cookies and French fries. The researchers also recorded what the children ate, plus their weight, body fat and waist size, at the start and again one year later.
The results were published on 23 October in the journal JAMA Network Open.
What they found
Children who ate more ultra-processed food showed a stronger response in the dorsal striatum, a part of the brain linked to reward and motivation. That stronger response went with bigger gains in BMI and body fat a year later. When the scientists took the brain response into account, the link between ultra-processed food and weight gain shrank by about a third for BMI and by almost half for body fat.
“This study goes beyond just understanding that UPFs affect weight gain,” said senior author Kathleen Page, hinting that the brain's reward system could be part of the path.
What it doesn't prove
This was an observational study, so it can't show that the food caused the brain changes or the extra weight. It was also small. The team is planning a follow-up in which children who usually eat a lot of these foods get more minimally processed meals instead.
It's a useful number to keep in mind: in the United States, ultra-processed foods make up about two thirds of the calories children eat each day. Swapping a few of them for home-cooked food is still the simplest experiment any family can try.