TOPLINE:

People who are obese burn calories in daily circadian cycles that are altered compared with those who are not obese, with the lowest point of energy expenditure occurring during their awake hours, as opposed to the typical lowest expenditures during sleeping hours observed among those of healthy weight.

Circadian patterns of glucose regulation are also altered among those who are obese, with key implications of the findings being potential clues in optimizing weight management approaches and reducing adverse effects of sleep regimens that counter the metabolic circadian patterns.

METHODOLOGY:

• The study involved 30 volunteers in healthy and obese weight ranges, who took part in a rigorous circadian protocol involving designated times of being awake and asleep and eating throughout each day for 5 days.

• Of the patients, 13 were of healthy weight (body mass index [BMI] > 25 kg/m2, and 17 were obese, defined as a BMI of 30 km/m2 or higher. They had a mean age of 48 and 14 were female.

• In addition to receiving regular blood, glucose and insulin testing, the participants took part in exercises while being monitored with an indirect calorimeter, which measures levels of exhaled carbon dioxide and estimates energy expenditure.

• After a baseline day of a normal sleep period, participants entered a “forced desynchrony” protocol to uncouple behaviors of sleep and wakefulness cycles from endogenous patterns in energy and glucose metabolism.

• Participants’ diets were standardized based on daily caloric requirements and identical in nutrient content. Meals and exercise testing sessions were distributed throughout the circadian cycle.

• Glucose and insulin assessment were performed in another subset of 19 participants, of whom 11 were male, seven were of healthy weight, and 12 were obese.

TAKEAWAY:

• Among those in the healthy weight group, the lowest period of energy expenditure, regardless of whether resting or exercising, occurred during the hours when the participant would habitually be sleeping.

• In contrast, among those who were obese, the lowest period of energy expenditure occurred during the period of typically being awake; however, their energy expenditure metrics were similar across circadian phases, without the adjustment of energy utilization during rest observed among those with healthy weight during the circadian night.

• Furthermore, those with obesity showed greater glucose intolerance during the circadian day, with lower insulin production during the circadian night.

• The obese group had higher carbohydrate vs fat utilization in exercising during the day; however, there were no significant differences across the circadian phase in either group for subjective hunger.

IN PRACTICE:

“It was surprising to learn how dramatically the timing of when our bodies burn energy differed in those with obesity,” first author Andrew W. McHill, PhD, of the Sleep, Chronobiology, and Health Laboratory, School of Nursing, Oregon Health & Science University, in Portland, said in a press statement.

“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.”

The authors add that “understanding these differences could help optimize weight-management approaches and reduce the adverse impact of shift work on body weight and metabolism to those with obesity.”

SOURCE:

The study was published November 15, 2023, in Obesity.

LIMITATIONS:

In addition to the small sample size being a limitation, some of the methodologies used, including a “forced desynchrony design” to evaluate metabolism outside of normal circadian patterns, could limit generalizability to other environments.

DISCLOSURES:

The study received funding from the National Institutes of Health. McHill reports consulting for Pure Somni Corporation. The other authors report no relevant financial relationships.

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