Higher resting-state activity in reward-related brain circuits in obese versus normal-weight females independent of food intake

BACKGROUND: In response to food cues, obese vs normal-weight individuals show greater activation in brain regions involved in the regulation of food intake under both fasted and sated conditions. Putative effects of obesity on task-independent low-frequency blood-oxygenation-level-dependent signals-that is, resting-state brain activity-in the context of food intake are, however, less well studied. OBJECTIVE: To compare eyes closed, whole-brain low-frequency BOLD signals between severely obese and normal-weight females, as assessed by functional magnetic resonance imaging (fMRI). METHODS: Fractional amplitude of low-frequency fluctuations were measured in the morning following an overnight fast in 17 obese (age: 39 +/- 11 years, body mass index (BMI): 42.3 +/- 4.8 kg m(-2)) and 12 normal-weight females (age: 36 +/- 12 years, BMI: 22.7 +/- 1.8 kg m(-2)), both before and 30 min after consumption of a standardized meal (similar to 260 kcal). RESULTS: Compared with normal-weight controls, obese females had increased low-frequency activity in clusters located in the putamen, claustrum and insula (P < 0.05). This group difference was not altered by food intake. Self-reported hunger dropped and plasma glucose concentrations increased after food intake (P < 0.05); however, these changes did not differ between the BMI groups. CONCLUSION: Reward-related brain regions are more active under resting-state conditions in obese than in normal-weight females. This difference was independent of food intake under the experimental settings applied in the current study. Future studies involving males and females, as well as utilizing repeated post-prandial resting-state fMRI scans and various types of meals are needed to further investigate how food intake alters resting-state brain activity in obese humans.