A study published in the journal Experimental physiology points out that people with an early chronotype use more fat during rest and exercise and have greater insulin sensitivity. They remain more physically active throughout the day and have a lower risk of type 2 diabetes.
Chronotype refers to an individual’s physiological preference to be active and alert at different times of the day. It influences a person’s sleep-wake cycle, physical activity, alertness, appetite, and core body temperature.
Early chronotypes (early risers) prefer to wake up and start their daily activities early in the morning. They tend to have a lower risk of cardiovascular and metabolic diseases. In contrast, late chronotypes (late risers) stay up late and feel more active and alert in the evening. They tend to have disturbances in energy metabolism and a higher risk of insulin resistance.
In the current study, scientists assessed the dynamics of energy metabolism among early and late chronotypes during rest and exercise.
The study population included 51 adults with metabolic syndrome. They were classified into early chronotypes (n = 24) or late chronotypes (n = 27) based on their response to a Morningness-Eveningness questionnaire.
Participants’ energy metabolism preferences were assessed by allowing them to perform moderate to high intensity exercise on a treadmill.
Carbohydrate and fat oxidation at rest and during exercise were determined to measure energy preference. In addition, heart rate and rating of perceived exertion were assessed. Physical activity profiles, body composition and insulin sensitivity for non-oxidative glucose disposal were also determined.
Analysis of metabolic parameters revealed that early chronotypes have higher VO2max (maximal oxygen utilization during exercise) and non-oxidative glucose disposal than late chronotypes.
The level of physical activity was higher in the early chronotypes. They were more active in the morning and midday compared to late chronotypes.
Under resting conditions, early chronotypes showed higher fat oxidation than late chronotypes. During moderate and high intensity exercise, both groups showed increased carbohydrate oxidation. However, early chronotypes maintained a higher level of fat oxidation during all exercise conditions.
During moderate exercise, maximal oxygen utilization was significantly correlated with fat oxidation and metabolic flexibility (carbohydrate or fat preference). A significant correlation was also observed between body mass index (BMI) and sedentary behavior in the afternoon.
Body weight and insulin sensitivity were significantly correlated with light physical activity. Notably, a significant correlation was observed between fat oxidation and non-oxidative glucose removal during high-intensity exercise.
Significance of the study
The study reveals that early chronotypes with metabolic syndrome use more fat during rest and exercise than their late chronotype counterparts. This metabolic activity in early chronotypes does not depend on fitness level and light physical activity per day.
Early chronotypes also have higher insulin sensitivity than late chronotypes, which reduces their susceptibility to type 2 diabetes. They remain less sedentary throughout the day and perform more physical activity in the morning and afternoon. noon, which further helps improve metabolic insulin sensitivity.
Although both early and late chronotypes may shift the energy preference toward carbohydrate oxidation during exercise, late chronotypes prefer carbohydrates over fat as an energy source.
As mentioned by the scientists, a variation in the patterns of the sleep-wake cycle and the circadian rhythm (internal biological clock) could be responsible for the metabolic differences between the early and late chronotypes.
Professor Steven Malin of Rutgers University, New Jersey, lead author of the study, said:
Night owls have a higher risk of obesity, type 2 diabetes and cardiovascular disease than early risers. One potential explanation is that they become misaligned with their circadian rhythm for a variety of reasons, but specifically in adults, it would work.
If late chronotypes are forced to wake up early due to workplace demands, they may feel more tired and sleepy throughout the day due to misalignment with their circadian pattern. This particular physiological pattern of people must be taken into account when considering the health risks of night shift work.
In this context, Professor Malin said,
If we favor a calendar pattern that is out of sync with nature, it could exacerbate health risks. Whether eating habits or activity can help alleviate them is an area that we hope will become clear over time.