Effects of Sleep Restriction on BAT Activation in Humans

The goal of this proposed research is to test the hypothesis that long-term mild sleep restriction (SR), as occurs frequently in adults and adolescents, leads to a positive energy balance and weight gain.

Aim 1. To determine the effects of SR, relative to habitual sleep (HS), on food choice and energy intake (EI) in adults at risk of obesity.

* Hypothesis 1a. EI, assessed by multiple weekly 24-hour recalls, will be greater during a period of SR relative to HS. This will be mostly due to increased fat and carbohydrate intakes. * Hypothesis 1b. Neuronal responses to food stimuli, assessed by functional MRI (fMRI) after 6 weeks of SR or HS, will indicate increased activity in networks associated with reward and food valuation (insula, orbitofrontal cortex) during a period of SR relative to HS. These responses will be correlated with intakes of high carbohydrate and high fat foods (hypothesis 1a) and neuropeptide Y (NPY). Moreover, activation of the default mode network (DMN) will be suppressed to a lesser extent after SR compared to HS.

Aim 2. To determine the effects of SR, relative to HS, on energy expenditure (EE) via independent and complementary approaches.

* Hypothesis 2a. EE, assessed by doubly-labeled water (DLW), and physical activity level, monitored daily by actigraphy, will be lower during SR relative to HS. * Hypothesis 2b. Brown adipose tissue (BAT), assessed by positron emission tomography and magnetic resonance combined scanner (PET/MR) using 18F-fluorodeoxyglucose (18FDG-PET) and fat fraction (FF) measurement under cold stimulation, will be greater after SR relative to HS. This would suggest higher adaptive thermogenesis after SR compared to HS. BAT activation will also be correlated with NPY.

Aim 3. To determine whether SR alters body weight and adiposity relative to HS.

* Hypothesis 3a. SR will lead to weight gain and increased total adiposity, as assessed using magnetic resonance imaging (MRI), relative to HS. * Hypothesis 3b. Increased adiposity after SR will be correlated to an adverse cardio-metabolic risk profile (increased glucose, insulin, triglycerides, leptin, reduced high-density lipoprotein cholesterol and adiponectin) and neuronal responses to food stimuli (Hypothesis 1b), and EE (Hypothesis 2a & 2b). Failure to stimulate BAT with SR will be associated with greater gain in adiposity.