Eating late has a number of negative effects, according to a new study out of the US. By eating late, you increase hunger levels, decrease caloric expenditure and cause negative changes to fat tissue.

Combined, all of these changes contribute to increased risk of obesity.

These findings are consistent with existing research on the negative effects of eating late, but they shed new light on exactly why doing so is bad.

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Eating late: negative effects

“We wanted to test the mechanisms that may explain why late eating increases obesity risk,” explained senior author Frank A. J. L. Scheer, PhD, 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?'” added first author Nina Vujovic, PhD, 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.”

The team worked with 16 women who were either overweight or obese according to their body mass index (BMI). Each woman completed two laboratory protocols: one with a strictly scheduled early meal schedule, and the other with the exact same meals, each scheduled four hours later in the day.

In the last two to three weeks before starting each of the in-laboratory protocols, participants maintained fixed sleeping schedules, and in three days before entering the laboratory, they were made to follow identical diets and meal schedules at home.

In the lab, participants regularly documented their hunger and appetite and provided frequent small blood samples throughout the day, as well as having their body temperature and energy expenditure measured. To measure how eating time affected molecular pathways involved in adipogenesis, or how the body stores fat, investigators took biopsies of adipose tissue from a subset of participants during laboratory testing in both protocols. This was done to enable comparison of gene expression patterns between these two eating conditions.

The results of the experiment revealed that eating late had profound effects on the hunger and appetite-regulating hormones leptin and ghrelin. Specifically, levels of the hormone leptin, which signals satiety (i.e. fullness), were decreased across the 24 hours in the late-eating protocol compared to the early-eating one.

When participants were eating late, they also burned calories at a slower rate and exhibited adipose tissue gene expression towards increased adipogenesis and decreased lipolysis, both of which promote fat growth. Notably, these findings convey converging physiological and molecular mechanisms underlying the correlation between eating late and increased obesity risk.

These new findings are not only consistent with a large body of research suggesting that eating later may increase one’s likelihood of developing obesity, but they shed new light on exactly why this might occur. By using a randomized crossover study, and tightly controlling for behavioral and environmental factors such as physical activity, posture, sleep, and light exposure, investigators were able to detect changes in the different control systems involved in energy balance, a marker of how our bodies use the food we consume.

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