The Weight on Young Minds
How Childhood Obesity Rewires the Developing Brain.
At a meeting of the European Association for the Study of Obesity in May 2025, a group of scientists from Austin, Texas, presented the findings of a study suggesting that the brains of children and teens whose bodies carry larger fat deposits in the abdomen differ structurally in key ways compared to kids the same age who don’t meet the criteria for what’s known medically as abdominal obesity (AO).
Using data from a subset of 3,320 youth who underwent MRI brain scans as part of the large-scale Adolescent Brain Cognitive Development (ABCD) Study, the researchers found that, on average, in kids with AO, the hippocampus and amygdala were 6.6% and 4.3% larger, respectively. (Kids were imaged twice, two years apart, so scientists could look at change over time.)
“These areas are related to emotional control and memory, and this could be a long-term effect,” said lead author Dr. Augusto César F. De Moraes, assistant professor of epidemiology at UTHealth Houston School of Public Health in Austin, Texas.
As if parents didn’t have enough to worry about when it comes to raising kids, the results of this trial are just one of the latest additions to a growing body of research that suggests higher body weight in childhood and adolescence may promote changes in the brain that could hold implications for brain health in later life.
“It’s certainly not the first report of obesity affecting brain health (in kids), but it’s a very large one, because it builds on this ABCD data,” noted Dr. Jack Virostko, one of the study co-authors and an associate professor of diagnostic medicine at the University of Texas at Austin’s Dell Medical School. Another strength of ABCD is that it comprises a treasure trove of data, he added. “You have all this brain imaging in parallel with blood tests, measurements of obesity and adiposity, surveys of risk-taking behaviour, and cognitive tests.”
THERE’S BEEN A LOT OF WORK ON UNDERSTANDING HOW OBESITY IN CHILDHOOD IS AFFECTING BRAIN FUNCTION AND BRAIN DEVELOPMENT, BECAUSE SO MANY CHILDREN
ARE NOW OBESE.
“Especially in the U.S.,” continued Dr. Kathleen Page, associate professor of medicine and pediatrics, co-chief of the Division of Endocrinology and Diabetes, and Director of the Diabetes and Obesity Research Institute at the Keck School of Medicine of USC (University of Southern California) in Los Angeles.(According to the U.S. Centers for Disease Control, roughly 20% of kids and youth aged two to 19 were living with obesity between 2017 and 2020. In Canada, from 2022 through 2024, 11% of kids aged five to 17 were classified as having obesity.)
Here, we’ll explore some of the key research findings, how scientists are trying to unpack whether obesity leads to brain changes or vice versa, and what may help ameliorate any potential negative effects and foster brain health from childhood onward.
ASSOCIATED CHANGES IN WHITE MATTER
One of the themes that has consistently cropped up across a range of papers is a link between measurements that estimate higher body weight and levels of body fat, such as body mass index (BMI) – which takes into account height and weight – and waist-to-hip ratio, and alterations in brain tissue known as white matter.
White matter is responsible for transmitting signals from one part of the nervous system to another, and it’s made up mostly of axons – the long “stems” that connect neurons in the brain that are wrapped in a sheath of fatty insulation called myelin.
“There are several studies by now that show there is
an association between higher body adiposity and some changes in white matter microstructure,” explained Dr. Zdenka Pausova, a professor in the Department of Pediatrics at the Université de Montréal, and a researcher at the Centre de recherche Azrieli at CHU Sainte-Justine. (One such paper, authored by Dr. Pausova and her team and published in Molecular Psychiatry in 2021, additionally showed that higher body adiposity is associated with lower cognitive processing speed.)
In the studies that Dr. Pausova is referring to, researchers observed specific features on magnetic resonance images of the brain, suggesting degradation of white matter in certain regions. For example, another study that used ABCD data, published in JAMA Network Open in 2023, found that higher BMI and waist circumference were associated with impairment in the integrity of the white matter in such areas as the corpus callosum (the main connection between the two hemispheres of the brain), and thinning of the outer layer of the brain or cortex (which is crucial for functions such as memory, learning, and problem-solving).
DIFFERENCES IN CIRCUITRY
Another type of scan known as resting-state functional MRI showed these same measurements of obesity were tied to decreased connectivity in areas of the brain that involve cognitive control and decision-making involving motivation and reward.
Brain changes that hint at differences in these abilities have been found across several studies, said Dr. Stephanie Kullmann, Group Leader and Deputy Head of Metabolic Neuroimaging at the Institute for Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Munich and the University of Tübingen, in Tübingen, Germany.
ONE THING THAT HAS EMERGED IS THAT THERE ARE TWO CIRCUITRIES OR SYSTEMS IN THE BRAIN THAT ARE STRONGLY AFFECTED BY OBESITY DURING CHILDHOOD – AREAS THAT ARE IMPORTANT FOR COGNITIVE PROCESSES AND REWARD REGIONS.
“The circuitries important for rewards seem to be altered in a way that these kids become more receptive and responsive to food cues. So they’re more prone to respond if there’s a visual cue or they have been rewarded with food, for example. But if they did get the food to eat, they feel less satisfied by it, which can be seen in the reward system – it’s a bit dampened,” she explained.
“Then we come to the more adolescent studies where different tasks are combined with neuroimaging, focusing on all kinds of decision-making processes, such as how they respond to commercials and make everyday life choices,” said Dr. Kullmann. “There, you can see that (adolescents) have a bit more of an issue of top-down control to make healthy choices if they’ve been exposed to obesity for longer themselves, or their parents have been.”
SOME EVIDENCE ALSO POINTS TO CONNECTIONS BETWEEN OBESITY AND LOWER SCORES ON CERTAIN TYPES OF TESTS AS WELL AS INCREASED RATES OF ANXIETY.
“Previous research in adults, and in children and adolescents – for example, the ABCD study – have looked at adiposity and cognitive functioning and anxiety,” Dr. Pausova explained. “It’s not just the cognitive functioning of the children, it’s also mood. There is quite good evidence in terms of seeing those cross-sectional relationships.”
UNRAVELLING RELATIONSHIPS
Since this type of research can’t provide cause and effect, some scientists are using other types of studies that could help explain how these different traits are related. For instance, researchers can use normal-weight kids who have parents with obesity, “as a sort of control group, to distinguish what is the effect of the body weight of the kid versus the effect of the obesity of the parents,” noted Dr. Kullmann.
AND YOU CAN ALREADY TELL THAT EVEN KIDS WHO ARE STILL LEAN, BUT THEIR PARENTS ARE OBESE, THAT ALREADY HAS AN EFFECT ON THEIR BRAIN CIRCUITRIES, MAKING THEM ALSO MORE VULNERABLE TO GAIN WEIGHT AT A LATER TIME POINT.
Both Dr. Kullmann and Dr. Page are interested in “not just asking the question how does obesity affect the brain, but what is it about obesity?” said Dr. Page. “Is it the diet? Is it inflammation? Is it insulin sensitivity?” (To help find answers, Dr. Page’s lab is following a cohort of 250 kids from age six or seven to age 20. One of her areas of focus is looking at children whose mothers had diabetes during pregnancy.)
For example, some research suggests that eating certain types of food, even for short periods, can cause undesirable effects. In one study Dr. Kullmann led, male college students in their 20s consumed high-calorie, ultra-processed foods for just five days. (The research was published in Nature Metabolism in 2025.)
“It was quite astonishing how the reward system got out of whack in the brain; specifically, they were learning a lot less from reward, which is a phenomenon we see in persons with obesity,” she noted. Participants also showed a key physical change: “The fat content in the liver went up.”
PEOPLE WITH HIGHER LEVELS OF BODY FAT, PARTICULARLY AROUND THE ORGANS DEEP WITHIN THE ABDOMEN (VISCERAL FAT), AND CHILDREN WHOSE MOTHERS HAD DIABETES DURING PREGNANCY ARE ALSO PRONE TO BEING LESS SENSITIVE TO THE EFFECTS OF INSULIN.
Some research suggests this insulin resistance is linked to specific brain differences independent of obesity. For example, in a study by Drs. Page and Kullmann, “we showed that children with insulin resistance basically have stronger connections in areas that are involved in processing rewards and motivation for food,” said Dr. Page. “That’s consistent with what’s been seen in children with obesity.”
Other physiological effects of higher levels of visceral fat may also at least partially explain some of the negative impacts of obesity on the brain. “We know that insulin resistance and inflammation affect brain function,” noted Dr. Page. “And we know that visceral fat has higher fat breakdown, which means higher amounts of free fatty acids floating around in the circulation. Visceral fat also releases more inflammatory cytokines.” (Cytokines are proteins that regulate inflammation.)
“Both of those things are strong factors that lead to insulin resistance and a number of (other) problems, like Type 2 diabetes,” Dr. Page added. And in later life, inflammation and insulin resistance are linked with an increased risk of dementia.
Dr. Pausova is probing the relationship between obesity and
brain changes from a different direction. “We studied mice during the age when the final maturation of the brain occurs,” when the whole brain is still growing, she explained. “We put the mice on a three-month high-fat diet to induce obesity, and did in vivo magnetic resonance imaging of the mouse brain. We observed that there is a decrease in the volume of the cerebral cortex and the hippocampus, but we were focused on the cortex.”
Next, “we took tissue samples from the regions within the cortex that had shown the greatest reductions in volume, and did single-cell RNA sequencing,” said Dr. Pausova. This allowed them to read the gene activity of individual cells. “We then analyzed the resulting data using a complex form of computerized technology called bioinformatics to identify individual cell responses to obesity induction.”
In essence, the results showed that resident immune cells in the brain (microglia) were activated and interacting with specific nerve cells in a way that suggested synaptic pruning, a culling of connections between nerve cells (synapses). At the same time, the activity of multiple cellular pathways that normally promote the sprouting and branching of new neurons was suppressed. Together, these changes could potentially explain why the cerebral cortex’s volume had shrunk.
SIMILARITIES TO ALZHEIMER’S
But what was the significance of the changes in gene activity patterns the researchers observed in the mice with induced obesity? Inflammation and cerebral cortex volume loss can occur in the brains of individuals with Alzheimer’s disease (AD). Dr. Pausova’s team took the single-cell RNA data from the mice and compared it against that of people with AD and controls from two published studies.
THE MICROGLIA THAT ARE THE DRIVERS OF NEUROINFLAMMATION SHOWED A STRIKINGLY SIMILAR PROFILE, MEANING THAT THE GENES
THAT WERE UPREGULATED BY OBESITY WERE EXPRESSED AT A HIGHER LEVEL IN ALZHEIMER’S AND VICE VERSA.
What’s more, when looking at the maps of cortex volume loss in human adolescents and adults, “the regions that showed the higher negative effect of the association by obesity were the regions that usually show greater loss of cortical tissue in mild cognitive impairment and Alzheimer’s disease,” Dr. Pausova explained. This research was published in the journal Brain, Behavior, and Immunity in 2024.
PROTECTIVE STRATEGIES
What does this mean for brain health over a lifetime? Without a great deal more research, there’s no way to know. But there are reasons to hope it’s possible to reverse such detrimental changes, preferably before kids reach adulthood. Our brains possess the capability to form new neural connections throughout our lives, and there is evidence that the same lifestyle habits that promote brain health in mid-life and beyond can likely do the same during childhood and adolescence.
“One of the things that we’ve seen in our studies is that children who exercise more, who are more physically active, had better brain development in terms of gray matter volume and they have stronger connections in pathways that are important for cognitive function and executive function, regardless of obesity,” said USC’s Dr. Page.
PHYSICAL ACTIVITY STIMULATES THE GROWTH OF BLOOD VESSELS THAT FEED THE BRAIN, AND STIMULATES GROWTH FACTORS
THAT ARE IMPORTANT IN PROTECTING NEURONS AND FOSTERING NEW NEURON GROWTH.
Limiting kids’ exposure to ultra-processed foods could be helpful, too. In Dr. Page’s research, “the more ultra-processed foods these children are eating, the stronger the connections in the reward pathways, which is predictive of increases in obesity over time,” she said.
Physical activity and a healthy diet also play important roles in fostering good cardiovascular health, which has been linked to some indicators of brain health in children and teens. In another study led by Dr. De Moraes, published in Mental Health and Physical Activity in 2024, the team found that kids with good cardiovascular health (as measured by such factors as blood pressure and blood cholesterol and such habits as sleep), had higher overall brain volume as well as, “higher volume in gray matter and white matter,” Dr. De Moraes explained. Kids with healthy cardiovascular profiles also scored better on tests that gauge performance in four domains of cognitive function: processing speed, memory, language, and executive function.
In other words, by engaging the whole family in habits that promote good cardiovascular health, we can probably protect our kids’ brain health, as well as our own.
Source: Mind Over Matter 22