Exercising in the morning may be the most effective way of burning fat, new research suggests.

Physical activity at the right time of the day seems able to increase fat metabolism, according to the study in mice.

It found that mice who exercised in an early active phase – which corresponds to morning exercise in humans – increased their metabolism more than mice that did exercise at a time when they usually rest.

Professor Juleen Zierath, from the department of molecular medicine and surgery and the department of physiology and pharmacology, Karolinska Institutet, Sweden, said: “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.”

Researchers say physical activity at different times of the day can affect the body in different ways as biological processes depend on the circadian rhythms of the cells – the 24-hour cycle that is part of the body’s internal clock .

To determine how the time of day affects the burning of fat, researchers at Karolinska Institutet and the University of Copenhagen studied the body fat of mice after a session of high-intensity exercise on a treadmill performed at two points of the daily cycle.

They looked at an early active phase and early rest phase – corresponding to a late morning and late evening session, respectively, in humans.

The scientists studied various markers for fat metabolism and analysed which genes were active in fat tissue after exercise.

They found that physical activity at an early active phase increased the expression of genes involved in the breakdown of fat (adipose) tissue, thermogenesis (heat production) and cells in the adipose tissue that indicate a higher metabolic rate.

According to the study, these effects were seen only in mice that exercised in the early active phase and were independent of food intake.

Prof Zierath added: “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.”

The findings are published in the PNAS journal.