A new study published in Nature Mental Health has found that different patterns of body weight over time are tied to distinct differences in brain structure, brain function, and cognitive abilities in adults. People whose obesity levels increased or stayed high over many years showed more brain abnormalities and lower cognitive performance, while those who lost weight or maintained low body fat levels had fewer signs of brain changes.
Although obesity has been connected to changes in the brain and cognition, most earlier research used only snapshots in time. Scientists were unsure whether the effects of obesity on the brain depend on how a person’s weight changes over the years. They also wanted to know if long-term patterns of obesity have different effects compared to short-term weight changes. To address these gaps, the team analyzed long-term health data and a wide range of body fat measurements, rather than relying only on body mass index, which cannot distinguish fat from muscle or show fat distribution.
“As we grow older, many of us start to wonder whether we can take control of our health to lead a better quality of life. The metabolic system plays a crucial role in overall health, including brain health. This sparked my interest in exploring how modifiable factors like obesity can influence brain function, and whether managing these factors proactively could help preserve cognitive health as we age,” explained study author Anqi Qui, a professor at the Hong Kong Polytechnic University (PolyU).
The study drew on data from the UK Biobank, a large research project that has followed over 500,000 people in the United Kingdom since 2006. For this analysis, the researchers focused on 50,538 participants who had detailed obesity measurements taken at two or three different time points across an average of nine years. These measurements included body mass index, waist circumference, waist-to-hip ratio, and fat percentages in different body regions. Brain scans and cognitive tests were also available for a subset of participants. After applying strict quality controls, about 24,000 participants were included in the brain imaging analysis and over 22,000 in the cognitive testing.
The team used advanced statistical techniques to identify five distinct patterns of obesity over time. About 25% of participants belonged to a “low-stable” group whose body fat stayed low across the years. Around 48% were in a “moderate-stable” group with stable but moderate obesity levels, while about 14% remained at high obesity levels (“high-stable”). Smaller groups either showed “increasing” obesity (about 8%) or “decreasing” obesity (about 6%).
When the researchers compared these groups, they found striking differences in brain structure. Participants who maintained low obesity levels showed the healthiest brain profiles. Those in the decreasing group, who lost weight over time, had minimal brain changes, with only small areas of thinning in the middle temporal and parahippocampal regions. In contrast, the increasing and stable obesity groups showed progressively greater thinning across the cortex, shrinkage in deep brain structures like the thalamus and putamen, and disruptions in brain network connectivity.
The most severe changes were seen in the high-stable group. These participants showed widespread thinning across almost the entire brain, reduced volumes in multiple subcortical areas, and disrupted communication across several brain networks, including those involved in movement, emotion regulation, and sensory processing. These patterns resembled brain changes typically associated with accelerated aging.
“I was surprised to find that a high level of obesity sustained over the long term may accelerate brain aging,” Qiu told PsyPost. “This highlights how chronic metabolic stress can have lasting impacts on brain health, beyond what we typically expect from physical health outcomes alone.”
Cognitive differences mirrored these brain findings. Compared to the low-stable group, individuals in the moderate-stable, increasing, and high-stable groups performed worse on tests of reasoning, working memory, and visuomotor speed. For example, people with consistently high obesity levels were slower at matching symbols to digits and performed worse on working memory tasks. Interestingly, some groups with higher obesity levels performed slightly better on visual memory tests, possibly reflecting different brain adaptations.
Mediation analyses suggested that changes in brain structure and function partially explained the links between obesity trajectories and cognitive performance. In particular, thinning of the cortex, reduced volumes in key brain regions like the thalamus and nucleus accumbens, and weakened network connections helped account for slower processing speeds and poorer memory in participants with higher or increasing obesity levels.
These findings provide evidence that “maintaining a healthy weight over the long term can have positive effects on brain health,” Qiu said. “Our findings suggest that managing body weight isn’t just important for physical health—it may also support better brain function as we age.”
The study had several strengths, including its large sample size, use of multiple body fat measurements, and comprehensive brain imaging and cognitive testing. However, there were also limitations. Most participants were middle-aged or older and of European descent, which may limit the generalizability of the findings to younger or more diverse populations. The study also relied on single brain imaging sessions rather than repeated scans over time, making it harder to track brain changes directly. In addition, only a few time points of obesity measurements were available, meaning that more complex patterns of weight change, such as repeated cycles of gain and loss, could not be fully captured.
“There are a few important limitations to consider,” Qiu said. “First, since the study is observational, we cannot draw conclusions about causality. Second, our findings are based on specific population cohorts, so further studies in more diverse groups are needed to confirm the generalizability of the results.”
Future research could expand these findings by examining more diverse populations, including younger adults, and by tracking both brain and body composition changes over longer periods. Studies could also explore whether interventions that promote weight loss or weight stability might help preserve brain health and cognitive function as people age.
“We aim to further investigate which specific regions of body fat have the greatest impact on brain health during aging,” Qiu explained. “Understanding these relationships in more detail could help identify targeted strategies to preserve cognitive function and promote healthy brain aging.”
The study, “Long-term obesity impacts brain morphology, functional connectivity and cognition in adults,” was authored by Die Zhang, Chenye Shen, Nanguang Chen, Chaoqiang Liu, Jun Hu, Kui Kai Lau, Zhibo Wen, and Anqi Qiu.