PORTLAND, Ore. — Weight loss can be a tough task for anyone, but obese individuals often find it especially difficult to shed excess pounds. Now, researchers from Oregon Health & Science University are shedding some much-needed light on the relationship connecting personal weight with how and when the body burns energy. Study authors say people with a generally healthy weight tend to use more energy during the day — when most people are active and eat. The obese, on the other hand, spend more energy during the night.
Importantly, researchers also note that during the day, obese individuals display higher levels of the hormone insulin, which is considered a sign that their bodies are working harder to use glucose, an energy-packed sugar.
“It was surprising to learn how dramatically the timing of when our bodies burn energy differed in those with obesity,” says the study’s first author, Andrew McHill, Ph.D., an assistant professor in the OHSU School of Nursing and the Oregon Institute of Occupational Health Sciences at OHSU, in a media release. “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.”
Obesity is technically defined as having a Body Mass Index (BMI) of 30 or higher. Studies continue to show that being either obese or overweight increases one’s risk of health conditions, including hypertension and Type 2 diabetes.
Daily schedules and rhythms, or when people tend to sleep, eat, and exercise, can also have a major impact on health; either by complementing or going against the body’s natural, daily rhythms. During every 24-hour cycle, people experience multiple changes triggered by the human body’s natural, internal clock. These daily changes usually occur at certain times of the day, all in an effort to best serve the body’s needs at any given hour.
McHill and this study’s senior author, Steven A. Shea, Ph.D., director of the Oregon Institute of Occupational Health Sciences at OHSU, specialize in researching how circadian rhythms and sleep impact the human body. McHill leads the OHSU Sleep, Chronobiology and Health Laboratory.
While earlier studies have indicated circadian rhythm misalignment affects energy metabolism and glucose regulation, those earlier projects mostly involved people with a healthy weight. So, in order to account for obese individuals specifically, researchers organized a study that included people of various body sizes.
In all, a total of 30 people volunteered to take part in the study. The project encompassed participants staying at a specially designed circadian research lab for six full days. Researchers were sure to follow a rigorous circadian research protocol featuring a schedule specially designed to keep participants awake and asleep at different times throughout each day.
Following each sleep period, volunteers were woken up to eat and participate in a variety of tests for the remainder of each day. One test asked participants to exercise while wearing a mask that was connected to a machine called an indirect calorimeter, which measures exhaled carbon dioxide and estimates energy used. The team collected blood samples in order to measure glucose levels in response to an identical meal provided each day.
Moving forward, study authors plan to continue exploring eating habits and hunger in people who are obese, as well as those of healthy weight. That new study will follow up on a 2013 study, also led by Shea, that found circadian clocks tend to naturally increase food cravings at night.
The study is published in the journal Obesity.
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