Sex-Related Differences Seen in Obese Individuals' Brains

Obesity is one of the most prevalent medical conditions today, and has a major impact on health. Recent neuroimaging studies have also shown a relationship between weight and brain structure. Obesity has been associated with a reduced total brain volume and diminished gray matter density.

Researchers from the Max Planck Institute for Human Cognitive and Brain Sciences (Leipzig, Germany),together with the department of endocrinology, University Clinic Leipzig (Germany), Integrated Research and Treatment Center Adiposity Diseases Leipzig, and the University College London (UK) have shown a gender-dependent relationship between being overweight and brain structure in the brain's white matter.

The investigators, who published their findings April 11, 2011, in the journal PLoS ONE, investigated the white matter brain structure of lean to obese men and women using diffusion-weighted magnetic resonance imaging (MRI) scanning. Using this technique, the movement of water molecules (diffusion) can be measured. As this motion is hindered by brain structures such as nerve fibers, changes in the white matter brain structures can be studied.

"Certain changes in the movement of the water molecules in brain tissue can indicate a reduced axonal or myelin density," said Dr. Karsten Mueller, the corresponding author of the study. Such changes were observed in the corpus callosum, a brain structure with 250 million nerve fibers connecting the left and the right hemisphere of the brain.

Axons are responsible for transmitting signals in the brain, and myelin is an insulating layer around the axons. With increasing body mass index (BMI), the mobility of the water changed, both along the nerve fibers and also across them. In both genders, the researchers discovered slower diffusion along the nerve fibers. In female participants only, they also found increased movement across the fibers. Both findings could indicate--possibly different--degeneration processes.

The differences in diffusion, which are also observed in premature aging of the brain tissue, were more dominant in female participants and covered a greater area of the corpus callosum. This is the first study to reveal systematic sex-related differences in the relationship between weight and the brain. This could possibly be because connections between the brain hemispheres generally show differences between men and women.

As yet, it is not clear which microstructural changes are actually present. Additional studies could bring provide clues, according to the researchers.

Related Links:
Max Planck Institute for Human Cognitive and Brain Sciences
University Clinic Leipzig
University College London