Obesity: You May Want To Rethink Eating Late

In America, approximately 42% of the adult population is living with obesity, and obesity is well-documented to contribute to the onset of serious chronic diseases including diabetes and cancer among others. Now research indicates that eating time affects how the body stores fat and regulates appetite hormones. 

"We wanted to test the mechanisms that may explain why late eating increases obesity risk," explained senior author Frank A. J. L. Scheer, Ph.D., Director of the Medical Chronobiology Program in the Brigham's Division of Sleep and Circadian Disorders. "Previous research by us and others had shown that late eating is associated with increased obesity risk, increased body fat, and impaired weight loss success. We wanted to understand why."

"In this study, we asked, 'Does the time that we eat matter when everything else is kept consistent?'" said first author Nina Vujovic, Ph.D., a researcher in the Medical Chronobiology Program in the Brigham's Division of Sleep and Circadian Disorders. "And we found that eating four hours later makes a significant difference for our hunger levels, the way we burn calories after we eat, and the way we store fat."

Participants in this study had a BMI in the overweight or obese range, and they completed two laboratory protocols either with strictly scheduled early meals or the other with the exact same meal but scheduled to be consumed four hours later. During the final 2-3 weeks before beginning each of the protocols, the participants maintained fixed sleep/wake schedules, and in the final 3 days before entering the lab they strictly followed identical diets and meal schedules at home. 

While in lab settings participants documented hunger and appetite, provided blood samples, as well as had testing to examine body temperature and energy expenditure. Additionally, biopsies of adipose tissue were collected to measure how eating time affected the adipogenesis molecular pathways during laboratory testing in both eating protocols to compare gene expression between the two eating conditions. 

According to the researchers, eating later has profound effects on the hunger and appetite-regulating hormones leptin and ghrelin. Levels of leptin were decreased across the 24 hours in the late eating group when compared to the early eaters who had more feelings of satiety. The late eaters also burned calories at a slower rate and exhibited adipose tissue gene expression of increased adipogenesis and decreased lipolysis which promotes fat growth. 

The researchers suggest that their findings convey converging physiological and molecular mechanisms underlying the correlation between eating late and the increased risk of obesity, and the findings may help to shed light on how eating later may increase this risk. 

Using a random crossover study and tightly controlling for environmental and behavioral factors the researchers were able to detect changes in the different systems involved in energy balance. 

"This study shows the impact of late versus early eating. Here, we isolated these effects by controlling for confounding variables like caloric intake, physical activity, sleep, and light exposure, but in real life, many of these factors may themselves be influenced by meal timing," said Scheer. "In larger scale studies, where tight control of all these factors is not feasible, we must at least consider how other behavioral and environmental variables alter these biological pathways underlying obesity risk. "