Dinner Time for Obesity and Prediabetes

This is a randomized, cross-over study that examines the metabolic impact of early vs late dinner, as defined by proximity of food intake to an individual's biological night as determined by dim light melatonin onset (DLMO) in normal-weight, healthy adult volunteers and in adults with obesity and prediabetes. Each participant will first undergo circadian phenotyping at the Johns Hopkins Bayview Clinical Research Unit (Baltimore, Maryland), with assessment of DLMO and core body temperature profile, as well as wrist actigraphy. Thereafter, participants will be crossover randomized to (1) a 24-hour metabolic chamber protocol where dinner is eaten 3 hours before DLMO (early dinner), or (2) a 24-hour metabolic chamber protocol where dinner is 1 hour eaten after DLMO (late dinner), both to be performed at the NIH Metabolic Clinical Research Unit (Bethesda, Maryland). The timing and nutritional contents of all meals, as well as sleep timing and duration, will be held constant. Oral \[2H31\] palmitate will be given with each dinner condition to quantify dietary fat oxidation. The 2 dinner conditions will occur in random order, with a 3- to 4-week washout period. The investigators are enrolling both Normal-Weight Healthy (NWH) and Obesity-Prediabetes (OPD) research participants. At this time (5/2023) the investigators are focusing on the NWH group.