The impact of body fat on our movements, emotions, and even the likelihood of developing Alzheimer’s disease varies based on its location within the body.

While many studies emphasize abdominal fat due to its correlation with cognitive decline and heart disease, few have explored fat distribution in other regions, usually with limited participant numbers.

To broaden understanding, Qiu from the Hong Kong Polytechnic University and her team investigated the effects of fat in the arms, legs, torso, and around internal organs on brain health.

The research team analyzed body composition scans and Brain Imaging data of over 18,000 adults with an average age of 62 involved in the UK Biobank Project. After taking age and other factors into account, they associated excess fat in different body regions with specific brain changes.

For instance, higher fat levels in the arms and torso correlated with thinning in the sensorimotor cortex, which is involved in movement. Increased arm fat was also linked to reduced hippocampal volume, a crucial area for memory that is traditionally affected in Alzheimer’s disease, potentially explaining why arm fat is associated with a higher risk of neurodegenerative disorders.

The researchers found that excess leg fat correlated with diminished connectivity in the brain’s limbic network, which is responsible for emotion and reward processing. This may be due to the fact that fat in the lower body releases leptin, a hormone that regulates hunger, with higher leptin levels connected to reduced limbic connectivity.

Conversely, visceral fat (around internal organs) was the type most strongly linked to functional changes in the brain, uniquely associated with white matter degradation—a characteristic of Alzheimer’s disease—rather than its preservation.

This may arise from the fact that visceral fat produces more inflammatory substances compared to fat located elsewhere in the body, according to Sonia Anand from McMaster University in Canada, which can contribute to brain inflammation.

It remains unclear why arm fat appeared to have both protective and detrimental effects on the brain. “Observing such divergent impacts was intriguing,” noted Mikal Schneider Biary from Rutgers University, New Jersey. This complexity underscores the intricate relationship between body fat and brain health, she added.

The research only established correlations between body fat and brain function, so “we can’t infer any causal connections,” Biary cautions. Some brain changes may indeed influence the distribution of body fat. Moreover, the findings might not apply to the broader population, as there was a notable lack of diversity among participants.

Nevertheless, the study emphasizes that different types and locations of fat exert varying effects, according to Anand. This suggests that treatments focusing on reducing visceral fat could have a more significant impact on brain health than generalized weight loss approaches.