The “Early Bird Gets the Worm” proverb from the 17th century refers to the advantage experienced by those who seize the opportunity at the earliest possible starting point. This may also translate into a lower risk of diabetes and heart disease, as new research published in Experimental Physiology reveals that the body’s preferences for using energy sources are altered by different sleep-wake cycles.

The scientists reported how sleep-wake cycles and one’s chronotype—our natural propensity to seek activity and sleep at various times—cause metabolic differences and alters our body’s preference for energy sources and how these preferences impact our health.

Steven Malin, PhD, senior author of the study and professor at Rutgers University, Piscataway, New Jersey, and colleagues explored how variations of circadian-mediated metabolic and hormonal profiles—described in their paper as either early or late chronotypes—impact insulin sensitivity and other metabolic health factors. Building on previous studies establishing that early chronotypes (ECs) are often insulin-sensitive, due in part to physical activity and lifestyle behavior, the researchers opted to take a deeper dive to see if chronotypes differ in resting and/or exercise fuel oxidation in relation to insulin action.

According to Dr. Malin, “The differences in fat metabolism between ‘early birds’ and ‘night owls’ shows that our body’s circadian rhythm (wake-sleep cycle) could affect how our bodies use insulin. A sensitive or impaired ability to respond to the insulin hormone has major implications for our health. This observation advances our understanding of how our body's circadian rhythms impact our health. Because chronotype appears to impact our metabolism and hormone action, we suggest that chronotype could be used as a factor to predict an individual’s disease risk.”

Using the Morningness–Eveningness Questionnaire (MEQ), the subject cohort of adults (n = 51) with metabolic syndrome (ATP III criteria) were classified as either EC (MEQ = 63.7 ± 0.9; n = 24 (19F), 54.2 ± 1.2 years) or late chronotype (MEQ = 47.2 ± 1.4; n = 27 (23F), 55.3 ± 1.5 years). Subjects consumed a calorie-controlled diet with required overnight fasting and were monitored for daily physical activity for a week. Body mass and composition were determined, and breath samples were used to measure fat and carbohydrate metabolism. Participants performed an incremental to maximal oxygen consumption test on a treadmill with self-selected walking speed maintained for the duration of the test. The incline was raised 2.5% every 2 minutes until the participant was unable to continue.

The researchers concluded that “Early chronotypes with metabolic syndrome utilized more fat during rest and exercise independent of aerobic fitness when compared with late chronotypes. Early chronotypes were also more physically active throughout the day. Greater fat use was related to non-oxidative glucose disposal. These findings suggest that early chronotypes have differences in fuel selection that associate with type 2 diabetes risk.”

“We also found that early birds are more physically active and have higher fitness levels than night owls who are more sedentary throughout the day. Further research is needed to examine the link between chronotype, exercise and metabolic adaptation to identify whether exercising earlier in the day has greater health benefits,” added Dr. Malin.

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