Analysis of MRI data from healthy participants has linked increasing body mass index (BMI) to cortical thinning in the right ventromedial prefrontal cortex and left lateral occipital cortex.
Previous findings on this relationship have been inconsistent. Nenad Medic, PhD, of the Department of Psychiatry at the University of Cambridge, and colleagues sought to clarify the association between obesity and its effects on brain structure by using surface-based morphometry to measure grey matter.
T1 magnetic resonance imaging (MRI) was obtained for 202 participants without significant medical history. BMI was calculated based on collected measurements for height and weight. MRI data was analyzed with surface-based morphometry to measure surface area, cortical folding, and cortical thickness.
The investigators found no association between participants’ BMI and global measurements of cortical thickness (t-value= -1.18, P=.24), total surface area (t-value=0.07, P=.95), or local gyrification index (t-value= -0.19, P=.85).
In the vertex-wise analysis, BMI was found to be negatively associated with cortical thickness in the left lateral occipital cortex (PMC=.0001) and the right ventromedial prefrontal cortex (PMC=.0001). The ventromedial prefrontal cortex is tied to goal-directed behavior and the lateral occipital cortex is associated with object recognition and visual attention. Post-hoc analysis further demonstrated significantly thinner cortices in these areas in obese (BMI ≥30) participants (P<.0001). However, cortical thickness in these areas was not significantly different in overweight (BMI ≥25 <30) or lean (BMI<25) participants.
The authors further note that the results did not indicate an age-by-BMI or gender-by-BMI interaction for differences in cortical thickness.
It is unclear from the results, however, if alterations in brain structure lead to increased BMI or adiposity causes the alterations to brain structure. They hypothesize that brain structure changes may be associated with several factors related to obesity including insulin resistance, low-grade systemic inflammation, leptin levels, and cortisol secretion.
“Our findings of regional thinning demonstrate that, even in younger adults with no known clinical morbidities, adiposity is associated with changes in cortical morphology,” the authors wrote. “The observation of vmPFC thinning in particular is highly consistent with the known functions of this region in value-based decision-making and mediating a balance between goal-directed and habitual responding.”
Medic N, Ziauddeen H, Ersche KD, et al. Increased body mass index is associated with specific regional alterations in brain structure. Int J Obes (Lond). 2016; doi:10.1038/ijo.2016.42.