BMI and Body Fat Mass Are Differentially Associated with fMRI Food‐cue Reactivity in Individuals with Obesity

Abstract

BackgroundBody Mass Index (BMI) is commonly used to categorize obesity in fMRI research. However, BMI fails to fully account for variability of body composition among individuals (e.g. body fat mass; BFM). Given that adipose tissue produces several hormones received by the brain to affect ingestive behavior, it is important to understand how BMI and BFM may be differentially associated with food‐cue reactivity in the brain.ObjectiveTo examine the association between both BMI and BFM with brain functional magnetic resonance imaging (fMRI) food‐cue reactivity (FCR).MethodsBaseline data of 32 subjects (age 19–65 yrs.; BMI 30–39.9kg/m2) was used from a larger study. BMI was calculated from measured height and weight and BFM was measured using bio‐electrical impedance. During the fMRI scan, subjects were shown 240 images (120 food and 120 objects) in an event‐related paradigm. Using the median BMI and BFM as the cut score, subjects were categorized into 2 groups (high and low), for both BMI and BFM. FMRI analyses were conducted on 3 levels in FSL to compare FCR: high BMI vs. low BMI and high BFM vs. low BFM.ResultsFMRI analysis revealed increased FCR in the high BMI compared to low BMI group in the bi‐lateral insular cortices. Increased FCR was seen in high BFM compared to low BFM group in the bilateral precuneus, left angular gyrus, left supramarginal gyrus, right orbitofrontal cortex, right nucleus accumbens, and the right temporal pole.ConclusionFCR was greater in both high BMI and high BFM groups compared with low BMI and low BFM groups. However the brain regions involved were different in each. These differences in FCR between BMI and BFM suggest a lack of concordance among these methods for delineating degree of obesity that may influence interpretation of fMRI FCR data. Given that BFM is more closely aligned physiologically with ingestion, it may be prudent to use BFM, not BMI, in fMRI FCR studies of obesity and ingestive behavior.Support or Funding InformationFunding: Nestle Health Science.