Your Brain Feels the Weight, Too: How Obesity Can Reduce Cognitive Ability

Chronic obesity can accelerate brain aging and impair important cognitive functions. Furthermore, the results of this study indicate that sustained obesity may serve as an early warning sign for the risk of cognitive decline, making it a possible marker for brain health. At the same time, the study carries a positive message: lifestyle changes that result in weight loss can have a significant impact on preserving brain function.

A large-scale study has revealed that long-term obesity is associated with a progressive decline in brain health, affecting both its physical structure and cognitive functions.

On the other hand, reducing excess weight over time may help preserve brain health, especially as we age. Given the continued rise in obesity rates worldwide, understanding how excess body fat influences the brain has become a priority for health researchers.

The relationship between obesity and the brain is complex. It involves changes in brain regions responsible for functions such as memory, attention, language and decision-making. Although it was already known that obesity affects the brain, there were still many questions about how this impact unfolds over time.

Most previous studies have assessed a person’s weight at just one point in their life, making it difficult to understand the true effects of chronic obesity.

To fill this gap, researchers from Hong Kong Polytechnic University conducted an in-depth study using longitudinal data, i.e. data collected over several years.

The study analyzed information from the UK Biobank, a British database of more than 500,000 participants aged 40 and over. From this information, they identified five distinct patterns of obesity over time:

1. Low-stable (constant low level of obesity)

   
   

2. Moderate-stable

   
   

3. High-stable

   
   

4. Increasing (progressive weight gain)

   
   

5. Decreasing (weight loss)

The researchers then compared these profiles with changes in the participants’ brain structure and cognitive performance.

The results showed that individuals who managed to reduce their obesity level over time (decreasing trajectory) experienced minimal effects on the brain, similar to those seen in people who were never overweight.

In contrast, those with persistent or increasing obesity experienced gradual and more significant impairments. In the increasing group, the negative effects began in areas of the brain linked to motivation and emotions.

In the moderately stable group, these effects extended to regions involved in language and memory. Specifically, the adverse effects extended from the fronto-mesolimbic regions in the increasing trajectory to the parietal and temporal regions in the moderately stable trajectory.

In contrast, in the highly stable group, who maintained high levels of obesity throughout the analyzed period, the brain changes were widespread.

These findings suggest that chronic obesity can accelerate brain aging and impair important cognitive functions. Furthermore, they indicate that sustained obesity may function as an early warning signal for the risk of cognitive decline, making it a possible marker for brain health.

At the same time, the study brings a positive message: lifestyle changes that result in weight loss can have a significant impact on preserving brain function.

Finally, the researchers emphasize the importance of monitoring body weight throughout life and promoting strategies for preventing and treating obesity, not only for its effects on the body, but also for the benefits it can bring to the mind.

Maintaining a healthy weight, or managing to reduce excess weight over time, can be an essential step in protecting the brain and ensuring healthier aging.

READ MORE:

Long-term obesity impacts brain morphology, functional connectivity and cognition in adults 

Die Zhang, Chenye Shen, Nanguang Chen, Chaoqiang Liu, Jun Hu, Kui Kai Lau, Zhibo Wen and Anqi Qiu

Nature Mental Health. 3, pages 466–478 (2025).

DOI: 10.1038/s44220-025-00396-5

Abstract

Although obesity has been implicated in brain and cognitive health, the effect of longitudinal obesity trajectories on brain and cognitive aging remains insufficiently understood. Here, using multifaceted obesity measurements from the UK Biobank, we identified five distinct obesity trajectories: low-stable, moderate-stable, high-stable, increasing and decreasing. We observed that individuals in the decreasing trajectory showed minimal adverse effects on brain structure and cognitive performance, compared with the low-stable trajectory (low obesity levels over time). By contrast, the increasing and moderate- and high-stable trajectories were associated with progressively greater impairments in brain morphology, functional connectivity and cognitive abilities. Specifically, adverse effects extended from fronto-mesolimbic regions in the increasing trajectory to parietal and temporal regions in the moderate-stable trajectory, culminating in widespread brain abnormalities in the high-stable group. These findings highlight the dynamic relationship between obesity evolution and brain-cognitive health, underscoring the clinical importance of long-term monitoring and management of obesity through a multifaceted approach.