Researchers at Oregon Health and Science University observed a striking pattern in energy use among individuals with obesity compared with those who maintain a healthy weight. The study, published in the journal Obesity, shows that obese participants tend to burn fewer calories during the day and more at night, while individuals with a healthier weight display the opposite pattern.
During the experiment, 30 adults with obesity spent six days in a laboratory designed to study circadian rhythms. Their sleep and wake cycles were deliberately varied to map how daily timing affects energy expenditure. Across all measurements, the obese group burned a greater share of calories at night than in the daytime. Caloric burn was tracked with a calorimeter, a device that estimates energy use by analyzing the amount of carbon dioxide exhaled. The study also found higher levels of the hormone insulin among obese participants, suggesting less efficient processing of glucose by their bodies.
Earlier research has shown that people of normal weight typically expend more energy during daylight hours. The exact triggers for the differences observed in energy patterns remain unclear. Lower daytime energy expenditure could contribute to excess weight, or it might be a consequence of it. Body mass index (BMI) is commonly used to assess weight status. BMI is calculated by dividing a person’s weight in kilograms by the square of their height in meters. A BMI above 30 is classified as obesity. Carrying extra weight raises the risk of conditions such as high blood pressure, certain cancers, and type 2 diabetes.
Beyond body weight, scientists continue to explore how daily timing influences metabolism and storage of fat. Some research suggests that misaligned circadian rhythms can affect hormone release and energy balance, potentially promoting fat accumulation in the liver and elsewhere. Understanding these dynamics may help in designing lifestyle interventions that align eating and activity with natural biological rhythms.
For individuals seeking to manage weight, a combination of regular physical activity, mindful meal timing, and adequate sleep emerges as a practical approach. Healthcare providers often emphasize that consistent routines and daytime activity support healthier energy use, while preventing late-night overeating that can disrupt metabolic processes. Lifestyle strategies that respect the body’s internal clock may enhance the effectiveness of weight management efforts and reduce the risk of metabolic disorders over time.
In sum, the research highlights a notable discrepancy in how energy is expended across the day in obese versus healthy-weight individuals. While the precise mechanisms remain under investigation, the findings contribute to a growing understanding of the relationship between circadian biology and metabolic health, underscoring the importance of aligning daily habits with natural bodily rhythms for better long-term outcomes.