Prolonged, Controlled Daytime versus Delayed Eating Impacts Weight and Metabolism.

A delayed eating schedule is associated with increased risk of obesity and metabolic dysfunction in humans. However, there are no prolonged, highly controlled experimental studies testing the effects of meal timing on weight and metabolism in adults with a body mass index (BMI) of 19-27 kg/m. Twelve healthy adults (age: 26.3 ± 3.4 years; BMI: 21.9 ± 1.7 kg/m; 5 females) participated in a randomized crossover study in free-living conditions. Three meals and two snacks with comparable energy and macronutrient contents were provided during two, 8-week, counterbalanced conditions separated by a 2-week washout period: (1) daytime (intake limited to 0800 h-1900 h) and (2) delayed (intake limited to 1200 h-2300 h). Sleep-wake cycles and exercise levels were held constant. Weight, adiposity, energy expenditure, and circadian profiles of hormones and metabolites were assessed during four inpatient visits occurring before and after each condition. Body weight, insulin resistance (homeostatic model assessment of insulin resistance [HOMA-IR]), trunk-to-leg fat ratio, resting energy expenditure, respiratory quotient, and fasting glucose, insulin, total and high-density lipoprotein (dHDL) cholesterol, and adiponectin decreased on the daytime compared to the delayed schedule. These measures, as well as triglycerides, increased on the delayed compared to the daytime schedule (effect size range: d = 0.397-1.019). Circadian phase and amplitude of melatonin, cortisol, ghrelin, leptin, and glucose were not differentially altered by the eating schedules. Overall, an 8-week daytime eating schedule, compared to a delayed eating schedule, promotes weight loss and improvements in energy metabolism and insulin in adults with BMI 19-27 kg/m, underscoring the efficacy and feasibility of daytime eating as a behavioral modification for real-world conditions.