The results are published in Cell Metabolism.
About 42% of adult Americans in the United States are obese, which increases the risk of developing chronic diseases like diabetes, cancer, and other illnesses.
Few studies have thoroughly examined the simultaneous effects of late eating on the three main players in body weight regulation and thus obesity risk. They are regulation of calorie intake, the number of calories you burn, and molecular changes in fat tissue. Popular healthy diet mantras discourage midnight snacking, but few studies have investigated the effects of late eating on all three players simultaneously.
A new study by investigators from Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system, found that when we eat significantly impacts our energy expenditure, appetite, and molecular pathways in adipose tissue.
“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.”
16 patients with a body mass index (BMI) in the overweight or obese range were examined by Vujovic, Scheer, and his team. Each participant underwent two lab protocols: one with a rigid early mealtime schedule and the other with identical meals served roughly four hours later in the day. Participants kept consistent sleep and waking schedules in the final two to three weeks before beginning each of the in-laboratory treatments, and in the final three days before entering the lab, they closely adhered to identical diets and meal times at home.
Participants underwent daily small blood sample administrations, regular recording of their hunger and appetite, body temperature monitoring, and energy expenditure testing in the lab. During laboratory testing in both the early and late eating protocols, researchers took biopsies of adipose tissue from a subset of participants to enable comparison of gene expression patterns/levels between these two eating conditions. This allowed them to measure how eating time affected molecular pathways involved in adipogenesis, or how the body stores fat.
The findings showed that eating later had significant impacts on the hunger and appetite-controlling chemicals leptin and ghrelin, which affect our desire to eat. Leptin levels, which indicate fullness, were specifically lower over the course of 24 hours in the late meal condition compared to the early feeding conditions. In addition to burning calories more slowly after eating, participants’ adipose tissue showed enhanced adipogenesis and decreased lipolysis, which encouraged fat growth. These results reveal similar physiological and molecular mechanisms that underlie the association between eating later in the day and a higher risk of obesity.
These results, according to Vujovic, not only support a wide body of research that suggests eating later may raise the risk of becoming obese, but they also provide new insight into how this can happen. Researchers were able to identify changes in the various control systems involved in energy balance, a sign of how our bodies use the food we eat, by using a randomised crossover study and strictly controlling for behavioural and environmental factors like physical activity, posture, sleep, and light exposure.
To make their findings more applicable to a larger population, Scheer’s team plans to increase the proportion of female participants in subsequent trials. Although there were only five female participants in this study cohort, the study was designed to account for the menstrual cycle, which reduced confounding but made it more challenging to find female volunteers. In the future, Scheer and Vujovic want to learn more about how the link between mealtime and nighttime affects 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. “