Amount of Fat Burned by Exercise Dependent on Time of Day

At least in mice, physical activity at the proper time of day appears to be able to improve the amount of fat burned. According to a recent study from the Karolinska Institutet in Sweden and the University of Copenhagen in Denmark, mice that exercised during an early active phase, which is comparable to a morning workout for people, had higher metabolisms than mice that exercised during a time when they would typically rest. The findings are presented in the PNAS publication.

Since biological processes rely on the circadian rhythms of the cells, physical activity at different times of the day can have varied effects on the body.

Researchers at Karolinska Institutet and the University of Copenhagen examined the adipose tissue of mice following a session of high-intensity exercise performed at two points of the daily cycle, an early active phase and an early rest phase, to determine how the time of day at which exercise is performed affects the burning of fat (corresponding to late morning and late evening session, respectively, in humans). The scientists examined numerous markers for fat metabolism and determined which genes were turned on in post-exercise adipose tissue.

Independent of Food Intake

The expression of genes involved in adipose tissue breakdown, thermogenesis (heat production), and mitochondria in the adipose tissue rose during early active phases of physical activity, the researchers discovered, suggesting a faster metabolic rate. Only mice that exercised during the early active period and independently of food intake showed these effects.

According to Professor Juleen R. Zierath of the Department of Molecular Medicine and Surgery and the Department of Physiology and Pharmacology at the Karolinska Institutet, “Our results suggest that late morning exercise could be more effective than late evening exercise in terms of boosting the metabolism and the burning of fat, and if this is the case, they could prove of value to people who are overweight,”

Boost the advantages of exercise for your health

Mice are a well-recognized model for the physiology and metabolism of humans because they share many fundamental physiological processes with humans. However, there are also significant distinctions, such as the nocturnal nature of mice.

The right timing seems to be important to the body’s energy balance and to improving the health benefits of exercise, but more studies are needed to draw any reliable conclusions about the relevance of our findings to humans,” says Professor Zierath.

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