An Oregon Health & Science University study that was released in the journal Obesity found that people who are at a healthy weight use more energy during the day, when most people are eating and being active. People who are obese, on the other hand, use more energy at night, when most people are sleeping. The study also discovered that people who are overweight or obese have higher amounts of the hormone insulin during the day. This means that their bodies are working harder to use glucose, a sugar that gives them energy.
“It was surprising to learn how dramatically the timing of when our bodies burn energy differed in those with obesity. 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.”
A Body Mass Index (BMI) of 30 or more means a person is obese. Health problems like high blood pressure and Type 2 diabetes are more likely to happen if you are overweight or fat.
When people sleep, eat, and work out can also have an effect on their health, either by working with or against their body’s normal daily rhythms. People go through many changes every 24 hours, which are caused by their bodies’ internal clocks. Some of these changes happen at certain times of the day so that they can best meet the needs of the body at any given time.
McHill and Steven A. Shea, Ph.D., director of the Oregon Institute of Occupational Health Sciences at OHSU and the study’s lead author, study how sleep and circadian rhythms affect the body. McHill is in charge of the Sleep, Chronobiology, and Health Laboratory at OHSU.
Previous studies have shown that an out-of-synchronized circadian cycle can change how energy is used and how glucose is controlled, but most of the people who took part in those studies were healthy weight. McHill, Shea, and coworkers set up a study with people of different body sizes to find out more about this.
Thirty people agreed to take part in the study. For six days, they stayed at a circadian research lab that was specially built for the purpose. The study strictly followed a circadian research plan that included a schedule that made sure people were awake and asleep at different times every day.
After each sleep period, volunteers were woken up to eat and take part in a range of tests for the rest of the day. In one test, people worked out while wearing a mask that was linked to a machine called an indirect calorimeter. This machine counts carbon dioxide released into the air and helps figure out how much energy is being used. Also, blood samples were taken to check how much glucose was in the blood after a meal that was the same every day.
Next, the researchers are going to look at how people who are overweight and people who are a healthy weight eat and feel hungry. The new study will also look into a study that Shea led in 2013 and found that circadian clocks naturally make people want to eat more at night.