Eating During This Time of Day Slows Calorie Burn and Weight Loss

|Updated Oct 12, 2022

Getty Images

If you wait until late in the day to eat most of your food, either because you aren't particularly hungry in the morning, or in order to intermittent fast or lose weight, a new study says you may be sabotaging your body's ability to burn more calories if that is one of your weight loss goals.

According to the research, fasting early and eating late in the day increases your hunger cues, decreases the number of calories your body burns, and even changes the way the body stores fat tissue to promote adding fat and decrease fat-burning as a means of survival.

Researchers at Brigham and Women's Hospital (part of Mass General in Boston) conducted the study to try and better understand the effect of late-day eating. They found that eating later impacted three key factors related to obesity and the ability to achieve weight loss: "regulation of calorie intake, the number of calories you burn, and molecular changes in fat tissue."

Late-Day Eating Impacts Weight Loss

Obesity afflicts approximately 42 percent of the U.S. adult population and contributes to the onset of chronic diseases, including type 2 diabetes, certain cancers, and metabolic conditions like insulin resistance and prediabetes.

The new study found that late eating suppresses the body's natural energy expenditure, drives up hunger (so you eat more when you finally tuck into dinner), and changes the structure of fat tissue, which in combination can increase your risk of obesity.

The timing of eating significantly impacts how much energy we burn throughout the day, as well as our appetite, and "molecular pathways in adipose tissue." Their results were just published in the journal Cell Metabolism.

"We wanted to test the mechanisms that may explain why late eating increases obesity risk," writes lead author Frank A. J. L. Scheer, Ph.D., who is Director of the Medical Chronobiology Program in Brigham's Division of Sleep and Circadian Disorders.

"Previous research ... had shown that late eating is associated with increased obesity risk, increased body fat, and impaired weight loss success. We wanted to understand why."

The study examined whether the timing of eating had an impact on obesity if all other factors stayed the same. It appears that late-day eating not only makes a difference in our circadian rhythm but also in the number of calories the body burns while fasting, as well as our hunger levels. But the most surprising finding was what happens to the molecular pathway of how the body stores fat.

It was a small study, with just 16 patients who were overweight or obese. Each participant adhered to a strict eating schedule of either early or late meals and kept all other factors constant including sleeping and waking times. By noting appetite and hunger, and taking blood samples and temperatures of participants throughout the day, the researchers could map energy expenditure.

To measure how eating time affected molecular pathways involved in adipogenesis, or how the body stores fat, investigators collected biopsies of adipose tissue from a subset of participants during laboratory testing in both the early and late eating protocols, to enable comparison of gene expression patterns/levels between these two eating conditions.

Late eating, defined as waiting four extra hours to begin eating for the day, promoted the release of the hunger hormone leptin, which stayed elevated for 24 hours, and also slowed the number of calories burned to do everyday activities. Late eating also promoted adipogenesis which is when the body stores fat, and lowered the rate of lipolysis, which is when the body mobilizes fat to burn for energy.

The study authors said their findings explain why waiting to eat (sipping breakfast and perhaps even lunch) set up individuals to gain fat, even though they are fasting. The body reacts to the lack of food by putting itself on a dimmer, to lower the output and preserve calories, and storing fat, as a way of self-protection against famine or other potentially life-threatening situations where food is scarce.

Bottom Line: Eat a Healthy Plant-Based Diet of High Fiber Meals All Day Long

Whether you are looking to lose weight or lower your risk of obesity and related diseases, eating a high-fiber diet of vegetables, fruit, legumes, whole grains, nuts, and seeds all day long is a proven way to stay full and lower your intake of calorie-dense foods like processed carbs. The worst thing to eat is a diet of refined carbs and added sugar, which spikes blood sugar and tells the body to store extra calories as fat.

For more on healthy eating and natural weight loss check out The Beet's Plant-Based Diet, created by a nutritionist.