A study conducted by Oregon Health & Science University, published in the journal Obesity, reveals notable differences in energy usage between individuals with a healthy weight and those with obesity. The research showed that people with a healthy weight tend to use more energy during the day, aligning with typical daily activities and meal times. In contrast, individuals with obesity were found to spend more energy during the night, generally a period of sleep for most.
The study, led by Andrew McHill, Ph.D., assistant professor at the OHSU School of Nursing and the Oregon Institute of Occupational Health Sciences at OHSU, also observed that during daytime hours, those with obesity exhibited higher levels of insulin. This elevation indicates that their bodies work harder to utilize glucose, a primary energy source.
Obesity, defined as having a Body Mass Index (BMI) of 30 or more, is associated with increased risks of health issues such as high blood pressure and Type 2 diabetes. The researchers, including McHill and senior author Steven A. Shea, Ph.D., director of the Oregon Institute of Occupational Health Sciences at OHSU, focus on how circadian rhythms and sleep influence the human body, particularly in relation to energy metabolism and glucose regulation.
The study involved 30 volunteers who stayed in a circadian research lab for six days, following a strict schedule designed to vary their wake and sleep times. The participants underwent various tests, including exercising with a mask connected to an indirect calorimeter, which estimates energy usage by measuring exhaled carbon dioxide. Blood samples were also taken to assess glucose levels in response to consistent meals provided each day.
The findings contribute to understanding how circadian rhythm misalignment affects energy metabolism, especially in individuals with different body sizes. Future research by the team plans to delve into eating habits and hunger in both obese and healthy-weight individuals. This upcoming study will also follow up on a 2013 study led by Shea, which highlighted natural circadian clocks’ role in increasing food cravings at night.
