Behavioral Chronotype: Impact on Sleep and Metabolism

The timing of food intake and caloric distribution across the 24hr day are emerging as contributing factors to weight gain. The idea that not only what you eat, but when you eat can contribute to weight gain has garnered interest from both the scientific community and the public. In fact, the distribution of caloric intake over the 24hr day has been recently recognized as a potential source of "circadian misalignment" which can result in adverse health outcomes, including overeating, impaired glucose tolerance, insulin sensitivity, and cardiovascular disease risk. This study will provide proof-of-concept evidence on the impact of misalignment on glucose metabolism and blood pressure regulation. This study will focus on overweight individuals who are at high risk of obesity but are still on a trajectory that can potentially be reversed by lifestyle changes. Following a careful assessment of the subject's habitual sleep and meal timing and caloric distribution under real life conditions, a short laboratory study will determine 24hr profiles of hormones involved in circadian timing, food intake and cardiovascular risk in a session that will mimic habitual sleep/wake and caloric distribution. Participants will then be randomized to one of three groups in which caloric distribution across the day will either be equally distributed between 3 meals, or heavily weighted to the morning or heavily weighted to the evening. During a 6-day semi-ambulatory in patient intervention, combining laboratory and ambulatory procedures, study procedures will assess the effect of experimentally changing caloric distribution across the day, advancing versus delaying the dietary chronotype. After 7 days of this caloric distribution intervention, we will then repeat the short laboratory session to assess whether the intervention of caloric distribution altered any of the measured profiles. The outcome measures will be the timing of the dim light melatonin onset (DLMO), blood pressure dipping, and insulin sensitivity. The proposed work will provide unambiguous evidence related to the efficacy of a novel lifestyle intervention - that could be more acceptable than dietary restriction or exercise - to reduce the risk of T2DM and CVD in adults at risk due to age and degree of adiposity. Moreover, our project will examine both middle-aged adults and older adults. The younger age group is of interest because of a lesser burden of illness and of an opportunity to alter the trajectory of aging at an earlier stage. The older age group is expected to have more severe circadian disturbances at baseline, with the potential of a larger effect on CM risk. The combined examination of metabolic risk and CVD risk in the context of circadian function is also novel.