Exercising before breakfast may burn twice as much fat, research suggests.
Scientists from the University of Bath looked at 30 overweight or obese men.
Over six weeks, some were told to work out before breakfast, while others exercised first thing.
The scientists found those who were active in the early hours burnt twice as much fat as those who ate beforehand.
Going without food overnight is thought to lower our insulin levels. Continuing to abstain from food may then cause the body to burn fat to fuel a work out, rather than sugar.
“Our results suggest changing the timing of when you eat in relation to when you exercise can bring about profound and positive changes to your overall health,” study author Dr Javier Gonzalez said.
“We found the men in the study who exercised before breakfast burned double the amount of fat than the group who exercised after.”
In England alone, 58% of women and 68% of men were overweight or obese in 2015, NHS Digital statistics show.
And in the US, more than two in three adults were carrying too much weight in 2013-14, according to the National Institute of Diabetes and Digestive and Kidney Diseases.
Studies looking into the best time of day to exercise have thrown up mixed results, with some suggesting morning larks lose the most weight, while others imply night owls shed more pounds.
To learn more, the Bath scientists had a group of men exercise either before or after breakfast. Others made no lifestyle changes and acted as “controls”.
Of those who worked out, their exercise regimens and diets were the same.
Results, published in the Journal of Clinical Endocrinology and Metabolism, show the men who exercised before breakfast were more responsive to insulin.
Insulin is a hormone produced by the pancreas that helps the body absorb glucose for energy. Failure to respond to insulin can trigger type 2 diabetes, which is associated with carrying too much weight.
“The group who exercised before breakfast increased their ability to respond to insulin, which is all the more remarkable given that both exercise groups lost a similar amount of weight and both gained a similar amount of fitness,” Dr Gonzalez said.
“The only difference was the timing of the food intake.”
The insulin levels of those who exercised after breakfast were no better than the controls’, the results show.
“This work suggests performing exercise in the overnight-fasted state can increase the health benefits of exercise for individuals, without changing the intensity, duration or perception of their effort,” co-author Dr Gareth Wallis, from the University of Birmingham, said.
“We now need to explore the longer-term effects of this type of exercise and whether women benefit in the same way as men.”