Obesity in teens alters brain regions tied to memory and emotion

A major study finds teens with abdominal obesity have enlarged brain areas linked to learning and emotion, raising concerns that excess weight and inequality may disrupt cognitive development and raise long-term dementia risk.

Study: National-level and state-level prevalence of overweight and obesity among children, adolescents, and adults in the USA, 1990–2021, and forecasts up to 2050. Image Credit: New Africa / Shutterstock

New research being presented at the European Congress on Obesity (ECO 2025) has found that several areas of the brain, including regions that play a critical role in learning and memory and the control of emotions, are larger in adolescents who are living with obesity.

The finding, from a study of thousands of teenagers in the US, raises concerns that obesity affects not only physical health but also learning, memory, and emotional control, says lead researcher Dr Augusto César F. De Moraes of UTHealth Houston School of Public Health in Austin, Department of Epidemiology, Texas, USA. "This is particularly alarming, given that the teenage years are such an important time for brain development," he adds.

The percentage of children and adolescents worldwide who are living with obesity more than quadrupled among girls (from 1.7% to 6.9%) and among boys (from 2.1% to 9.3%) between 1990 and 2022.

In the US, it is estimated that more than one in three children aged 5 to 14 (36.2% of boys and 37.2% of girls) are living with overweight or obesity, equating to more than 15 million children.

Obesity – particularly abdominal obesity – has been linked to changes in brain development in the past, with regions key to cognition and the regulation of emotions seemingly particularly vulnerable.

Health inequalities, such as poor access to quality education, safe neighbourhoods, and healthy food, are well-known contributors to physical health problems, but their role in brain development and cognition is often overlooked.

To learn more about how obesity and health inequalities affect brain structure and cognition, Dr De Moraes and colleagues in the US, Brazil, and Spain analysed data from 3,320 participants in the ABCD study, an ongoing research project into how childhood experiences affect brain development and health.

The participants were recruited from cities in 17 states and followed for four years, from 2016 to 2018 and 2020 to 2022.  The average age of participants at baseline was 9.9 years, and 47.4% were girls.

They were categorised based on their obesity status, further stratified by abdominal obesity (measured using waist circumference). At baseline, approximately 34.6% of participants were classified as having abdominal obesity.

Structural MRI scans assessed the volume of several brain regions of the brain's subcortex, including the amygdala, hippocampus, caudate, accumbens, pallidum, putamen, and thalamus.

Health disparities were assessed using the Child Opportunity Index, which measures a child's opportunities based on the quality of neighbourhood features such as education, walkability, and access to healthy food and green space.

Several brain regions were larger in adolescents with abdominal obesity than in their peers without abdominal obesity. The biggest changes were seen in the hippocampus, which is involved in memory and learning, and the amygdala, which regulates or controls emotions, including fear, happiness, anger, and anxiety.

The hippocampus was approximately 6.6% larger, and the amygdala was about 4.3% larger in teens with abdominal obesity compared to those without.

The amygdala was particularly large in teenagers with very high levels of abdominal fat (a waist-to-height ratio over 0.5). The researchers raise concerns that excess body fat affects how the brain handles emotions.

The thalamus (which relays information about movement, hearing, taste, sight, and touch) and caudate (which helps control movement) showed smaller increases in size.

The study also found that teens from lower-opportunity areas showed reduced development in key brain regions, such as the hippocampus, putamen, and amygdala, compared with their peers in higher-opportunity areas. "This difference was even more pronounced among adolescents with persistent abdominal obesity," says Dr De Moraes. "It highlights the urgent need to address both social inequality and health risks to support not only physical wellbeing but also healthy brain development in youth."

The authors explain that in the context of the young developing brain, both decreased and increased growth can cause harm. Thus, having lower-than-normal brain development, as shown in the teens in lower-opportunity areas, or larger-than-normal parts of the brain due to inflammation caused by obesity, can both be harmful.

Dr De Moraes concludes: "Our findings suggest that obesity, particularly abdominal obesity, can impair teenagers' learning, memory, and emotional control. I worry about how these changes, which are occurring at the age of 13 or 14, might affect them later in life.

"There's even a chance they could be at a higher risk of things like memory problems or dementia as they get older.

"That's why we believe supporting healthier habits early on is so important, not just for physical health, but for brain health too.

"Treating and preventing adolescent obesity won't only improve health – it may improve brain health, too."