The foods children eat may influence more than their waistlines. A new study suggests that diets high in ultra-processed foods (UPFs) are associated with heightened activity in brain regions involved in reward and motivation, potentially helping explain why some children gain more body fat over time. The findings, published in JAMA Network Open, offer new insights into how everyday eating habits may relate to the developing brain.

Ultra-processed foods, including packaged breads, breakfast cereals, instant soups and ready-made snacks, are typically manufactured for convenience, long shelf life and appealing taste. They often contain additives such as artificial sweeteners, colours and flavourings. These products have become a major part of children’s diets, accounting for approximately 67% of daily calorie intake among American children.

Previous research has linked high consumption of ultra-processed foods to obesity, type 2 diabetes and cardiovascular disease. However, scientists have struggled to understand the biological mechanisms behind these associations, particularly how the brain’s reward system responds to tempting foods during childhood.

Researchers at the University of Southern California examined 46 children aged seven to 10 who were participating in the long-term BrainChild study. All were initially at a healthy weight. The team collected dietary information, body measurements, and magnetic resonance imaging (MRI) scans while the children viewed photographs of appetising foods, including biscuits and French fries. Their weight-related measurements were assessed again one year later.

Children who consumed more ultra-processed foods showed greater activity in the dorsal striatum, a brain region associated with reward and motivation, when viewing food images. Stronger activity in this region was also linked to greater increases in body mass index (BMI) and body fat percentage over the following year.

The researchers found that higher UPF consumption was associated with greater BMI, body fat percentage and waist circumference at follow-up. When differences in brain responses were taken into account, the associations with BMI and body fat percentage weakened by 31% and 44%, respectively. This suggests that heightened sensitivity to food cues may partly explain the relationship between ultra-processed diets and weight gain.

“Children’s brains are still developing, habits are still forming and food preferences are still being made,” said senior author Dr Kathleen A. Page, professor of medicine and paediatrics at USC’s Keck School of Medicine. She emphasised that improving children’s diets requires more than individual choices, particularly when ultra-processed products are often cheaper, more convenient and more readily available than healthier alternatives.

The researchers caution that the observational study cannot establish cause and effect. Future experiments will investigate whether replacing ultra-processed foods with minimally processed alternatives changes children’s brain responses and reduces weight gain. Meanwhile, the BrainChild study will continue following participants through puberty and into young adulthood, offering further insights into how childhood diets may shape long-term brain development and metabolic health.

More information: Jasmin M. Alves et al, Ultraprocessed Food Intake, Striatal Response to Food Cues, and Adiposity Gain in Children, JAMA Network Open. DOI: 10.1001/jamanetworkopen.2026.40252

Journal information: JAMA Network Open Provided by Keck School of Medicine of USC