Time-restricted feeding (TRF) is a form of intermittent fasting that involves having a longer daily fasting period. Preliminary studies report that TRF improves cardiometabolic health in rodents and humans. Here, we performed the first study to determine how TRF affects gene expression, circulating hormones, and diurnal patterns in cardiometabolic risk factors in humans. Eleven overweight adults participated in a 4-day randomized crossover study where they ate between 8 am and 2 pm (early TRF (eTRF)) and between 8 am and 8 pm (control schedule). Participants underwent continuous glucose monitoring, and blood was drawn to assess cardiometabolic risk factors, hormones, and gene expression in whole blood cells. Relative to the control schedule, eTRF decreased mean 24-hour glucose levels by 4 ± 1 mg/dl (p = 0.0003) and glycemic excursions by 12 ± 3 mg/dl (p = 0.001). In the morning before breakfast, eTRF increased ketones, cholesterol, and the expression of the stress response and aging gene SIRT1 and the autophagy gene LC3A (all p < 0.04), while in the evening, it tended to increase brain-derived neurotropic factor (BNDF; p = 0.10) and also increased the expression of MTOR (p = 0.007), a major nutrient-sensing protein that regulates cell growth. eTRF also altered the diurnal patterns in cortisol and the expression of several circadian clock genes (p < 0.05). eTRF improves 24-hour glucose levels, alters lipid metabolism and circadian clock gene expression, and may also increase autophagy and have anti-aging effects in humans.

Intermittent fasting (IF) is the practice of alternating eating and extended fasting. In recent years, IF has been touted for losing weight and body fat. Indeed, IF can decrease body fat and preserve lean mass in animals and humans.^1-11 Moreover, a few clinical trials have reported that IF is better for losing weight and/or body fat than continuous energy restriction in the short term.^3,6,12-16 However, the literature is mixed, and there is no definitive evidence that IF selectively burns body fat while sparing muscle tissue.

A large international effort is underway to reduce childhood obesity in response to increasing rates of obesity among children and adolescents.^1-3 Accurate classification of excess body fat is central to these efforts. As of 2017, body mass index (BMI), calculated as weight in kilograms divided by height in meters squared, is used worldwide to screen for obesity.