Most folks are more likely to use their energy eating and exercising during daylight hours. But the bodies of people with obesity are on a different schedule. They burn more of their energy during the night hours.

The Oregon Health & Science University (OHSU) study discovered something else: Those with obesity have higher levels of the hormone insulin during the day, a sign that the body is working harder at this time to use glucose — the main type of sugar in our blood and the major source of energy for our body’s cells.

Obesity is defined as excessive or abnormal fat accumulation that presents a risk to health including the conditions high blood pressure, Type 2 diabetes, certain cancers and dementia. One of the indications of obesity is a Body Mass Index (BMI) of 30 or more.

“It was surprising to learn how dramatically the timing of when our bodies burn energy differed in those with obesity,”

“It was surprising to learn how dramatically the timing of when our bodies burn energy differed in those with obesity,” the study’s first author, Andrew McHill, an assistant professor in the OHSU School of Nursing and the Oregon Institute of Occupation Health Sciences at OHSU, said in a press release.

But there was a catch-22 as McHill points out: “However, we’re not sure why. Burning less energy during the day could contribute to being obese, or it could be the result of obesity.”

Thirty participants volunteered to stay for six days and nights at a specially designed circadian rhythm research lab. Circadian rhythms are the physical, mental and behavioral changes that follow a 24-hour cycle. These natural processes respond primarily to light and dark and affect not only humans, but other animals, plants and microbes.

The research team followed a protocol that involved a specific schedule designed to have participants be awake and asleep at different times throughout each 24-hour period. After each period of sleep, the volunteers were awakened so they could eat and participate in a variety of tests for the remainder of the day.

One test had the participants exercise while they were wearing a mask that was hooked up to a calorimeter, which measures exhaled carbon dioxide and helped to estimate how much energy was being used. Blood samples were also collected to measure how glucose levels responded to an identical meal provided during each day.

Those with obesity have higher levels of the hormone insulin during the day, a sign that the body is working harder at this time to use glucose.

They found that people with obesity not only appear to burn less energy during the day, but they may also have slower metabolisms. Both can not only contribute to weight gain, but also difficulty dropping extra pounds. The study also underscores the importance of addressing metabolic differences when developing a treatment plan for those with obesity.

Scientists are hopeful that continued investigation in this area will lead to effective strategies for the prevention and management of obesity. For now, the best way to deal with losing weight is to eat a healthy, reduced-calorie diet and exercise regularly, though some may find the new weight-loss drugs or bariatric surgery helpful. Speak with your healthcare care provider about a safe weight loss management program.

The study is published in the journal, Obesity.