Abstract
It is well established that obesity decreases overall life expectancy and increases the risk of several adverse health conditions. Mounting evidence indicates that body fat is likely also associated with structural and functional brain changes, reduced cognitive function, and greater impulsivity. However, previously reported differences in brain structure and function have been variable across studies and difficult to reconcile due to sample population and methodological differences. To clarify these issues, we correlated two independent measures of body composition—i.e., body mass index (BMI) and body fat percent (BFP)—with structural and functional neuroimaging data obtained from a cohort of 32 neurologically healthy adults. Whole-brain voxel-wise analyses indicated that higher BMI and BFP were associated with widespread decreases in gray matter volume, white matter volume, and white matter microstructure (including several regions, such as the striatum and orbitofrontal cortex, which may influence value assessment, habit formation, and decision-making). Moreover, closer examination of resting state functional connectivity, white matter volume, and white matter microstructure throughout the default mode network (DMN), executive control network (ECN), and salience network (SN) revealed that higher BMI and BFP were associated with increased SN functional connectivity and decreased white matter volumes throughout all three networks (i.e., the DMN, ECN, and SN). Taken together, these findings: (1) offer a biologically plausible explanation for reduced cognitive performance, greater impulsivity, and altered reward processing among overweight individuals, and (2) suggest neurobiological mechanisms (i.e., altered functional and structural brain connectivity) that may affect overweight individuals' ability to establish and maintain healthy lifestyle choices.
Highlights
IntroductionObesity affects more than 850 million people (i.e., 10% of men and 14% of women) worldwide (Finucane et al, 2011), is a major risk factor for many serious health conditions—including type II diabetes (Kahn et al, 2006), cardiovascular disease (Hubert et al, 1983), hypertension (Rahmouni et al, 2005), sleep apnea (Vgontzas et al, 1994), and cancer (Calle and Kaaks, 2004)—and is thought to be one of the greatest contributors to preventable death in the United States (Flegal et al, 2005; Jia and Lubetkin, 2010)
Participants in our sample spanned a wide range of body mass index (BMI) and body fat percent (BFP) values (Figure 1 and Figure S1)—including categorically underweight, normal weight, overweight, and obese individuals—which enabled individual differences in body composition to be correlated with functional connectivity, gray and white matter morphology, and white matter microstructure
salience network (SN) connectivity showed marginally significant positive correlations with both BMI and BFP, even after correcting for multiple comparisons (Figure 2D; padj. = 0.07 and padj. = 0.09, respectively), such that higher BMI and BFP were associated with greater SN connectivity
Summary
Obesity affects more than 850 million people (i.e., 10% of men and 14% of women) worldwide (Finucane et al, 2011), is a major risk factor for many serious health conditions—including type II diabetes (Kahn et al, 2006), cardiovascular disease (Hubert et al, 1983), hypertension (Rahmouni et al, 2005), sleep apnea (Vgontzas et al, 1994), and cancer (Calle and Kaaks, 2004)—and is thought to be one of the greatest contributors to preventable death in the United States (Flegal et al, 2005; Jia and Lubetkin, 2010). One study has reported gray matter increases (rather than decreases) in the orbitofrontal cortex, nucleus accumbens, putamen, and hypothalamus (Horstmann et al, 2011)
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