A compelling new study published in JAMA Network Open has shed light on a biological mechanism that may help explain the complex relationship between ultra-processed foods (UPFs) and childhood obesity. Researchers have discovered that children who consume higher amounts of these products demonstrate heightened activity in the brain’s reward centers when exposed to images of appetizing foods. Furthermore, these amplified neural responses appear to correlate with significant increases in body fat and body mass index (BMI) over the course of a year, offering a potential neurobiological explanation for why these diets are so difficult to abandon.
Ultra-processed foods—a category that includes an array of common supermarket staples such as pre-packaged breakfast cereals, processed breads, instant soups, and various snack products—have become a dominant fixture in the modern diet. Engineered for convenience, long shelf life, and hyper-palatability, these foods frequently contain a complex mixture of artificial sweeteners, synthetic coloring agents, and additives that are rarely found in traditional home cooking. The ubiquity of these products is staggering; in the United States, they account for approximately 67% of the total calories consumed by children.
For years, the medical community has recognized a strong statistical association between the consumption of UPFs and the prevalence of chronic health conditions, including obesity, type 2 diabetes, and cardiovascular disease. Yet, despite these well-documented links, the precise biological and neurological processes that drive these outcomes have remained elusive. The new investigation, supported by the National Institutes of Health, sought to bridge this gap by integrating magnetic resonance imaging (MRI) with rigorous dietary assessments and physical body composition measurements. The goal was to determine if the brain’s reward system plays a mediator role in how children process food cues and how that processing translates into physical changes over time.
"Children’s brains are still developing, habits are still forming, and food preferences are still being made," explained Dr. Kathleen A. Page, the study’s senior author. Dr. Page serves as a professor of medicine and pediatrics and is the co-chief of the Division of Endocrinology and Diabetes at the Keck School of Medicine of USC. "It’s an important period where the brain is very sensitive to food and the food environment. We’re particularly interested in understanding these processes in children, because we believe that intervening early could make a real difference."
Brain Scans Reveal a Link to Future Weight Gain
To explore these neurological pathways, the research team recruited 46 children between the ages of seven and 10 who were already participating in the long-term "BrainChild" study—an ongoing research initiative focused on identifying the precursors to diabetes and obesity in youth. A critical design feature of this study was that all participants were of a healthy weight at the outset. This allowed the researchers to observe potential "warning signs" in the brain and metabolic profile before the onset of excess weight gain, rather than analyzing children who had already developed obesity.
At the beginning of the study, the children underwent sophisticated brain scans while viewing high-contrast photographs of tempting, calorie-dense foods, such as French fries and cookies. During this session, the researchers simultaneously collected comprehensive data on the children’s diets and recorded a suite of baseline physical health markers, including BMI, body fat percentage, and waist circumference. Twelve months later, the team invited the participants back to repeat these measurements to identify any physical shifts that occurred during the year.
The resulting neuroimaging data revealed a striking pattern: children who reported higher daily intake of ultra-processed foods exhibited significantly greater activation in the dorsal striatum when viewing the food images. The dorsal striatum is a deep-seated region of the brain responsible for regulating reward, motivation, and habit formation. Its heightened response to food cues suggests that children with higher UPF consumption may experience a more intense psychological and physiological "pull" toward tempting foods.
More significantly, this neurological pattern was predictive of physical changes. Children who demonstrated the strongest responses in the dorsal striatum were also those who experienced the most substantial increases in BMI and body fat percentage over the following year. This suggests that a heightened neural sensitivity to food cues may be a critical link in the chain that connects ultra-processed diets to the development of obesity.
How Brain Reward Activity May Influence Body Fat
By the end of the one-year study, the researchers observed that children who consumed more ultra-processed foods generally presented with higher BMI, a higher percentage of body fat, and larger waist circumferences compared to their peers. To determine whether brain activity was the primary driver of these changes, the team conducted a mediation analysis.
When the researchers adjusted their statistical models to account for the children’s neural responses in the dorsal striatum, the strength of the relationship between ultra-processed food intake and BMI dropped by 31%. Similarly, the association between diet and body fat percentage decreased by 44%. These reductions provide compelling evidence that the brain’s reward response acts as a significant mediator in the relationship between diet and physical health outcomes.
While these findings do not definitively prove that ultra-processed foods cause direct, structural alterations to the brain—as the study was observational—they provide a robust biological framework for understanding the observed associations. "This study goes beyond just understanding that UPFs affect weight gain," Dr. Page noted. "It actually gives us insight into the neurobiological underpinnings by which these foods may be linked to body composition over time."
Making Healthier Foods More Accessible
The research team is careful to emphasize that the responsibility for dietary health does not rest solely on the shoulders of individual families. Ultra-processed products are often the most economically viable option for households, as they are frequently cheaper, more widely available in "food deserts," and easier to prepare for busy parents balancing work and home life.
"Changing the food environment to help people access healthier, more minimally processed foods is an important part of the solution," Dr. Page said. She argues that systemic changes are necessary to shift the needle on childhood health, rather than relying on parents to navigate an environment that heavily favors inexpensive, calorie-dense products.
Despite the strength of the findings, the researchers acknowledge several limitations. Because the study was observational in nature, it cannot establish a direct causal pathway from consuming ultra-processed foods to the observed brain changes or weight gain. It is possible, for instance, that children with certain brain profiles are predisposed to prefer ultra-processed foods, or that other environmental factors play a larger role. To address these questions, Dr. Page is planning a future intervention study. This research would provide children who regularly consume high levels of UPFs with healthier, minimally processed alternatives to see if changing the diet can "reset" the brain’s response to food images and slow or reverse the associated weight gain.
In the meantime, the BrainChild study remains ongoing. Researchers plan to continue tracking the participants as they navigate the biological and psychological shifts of puberty and progress into early adulthood. By maintaining this longitudinal perspective—monitoring the interplay between brain development, body composition, and shifting dietary patterns—the team hopes to provide a clearer, more comprehensive map of how nutrition in early childhood influences long-term health trajectories.
The research was conducted by a dedicated team at the Keck School of Medicine of USC, including Jasmin M. Alves, Ella Morgan, Brendan Angelo, Kianna Le, and Jared Smith, along with contributors from the USC Stevens Neuroimaging and Informatics Institute and Kaiser Permanente Southern California. The work was made possible through funding from the American Diabetes Association and the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health.
