Exercising on an empty stomach could be better for you than doing so after a meal, according to a study.
Men who had a workout before breakfast lost more fat than those who did so after the first meal of the day, scientists found.
There might be an extra benefit from exercising before eating, although further study is needed to assess the longer-term effects.
The study was carried out by Dr Jason Gill and Nor Farah of the Institute of Cardiovascular and Medical Sciences at the University of Glasgow.
Ten overweight men who were not regular exercisers took part in the study which looked at the effects of exercising before and after breakfast on metabolic health and fat loss.
Each man underwent three trials, up to a fortnight apart. In one, they performed no exercise then ate breakfast. The other trials saw them walking briskly for 60 minutes before eating breakfast, or doing the same walk after eating their morning meal.
Participants were given lunch three and a half hours after breakfast and the amount of fat their body burnt and the level of fat, sugars and insulin in the blood were measured over an eight and a half-hour period on each occasion.
Both periods of exercise increased fat-burning over the day, the results indicated.
But exercise before breakfast resulted in greater fat loss and larger reductions in the level of fat in the blood.
Dr Gill said: "Any exercise you do is beneficial but the indications are that there might be an extra benefit associated with exercising before eating, compared to after. However, further study is needed to determine whether the present findings extend over the long term.
"In the end we would like to encourage everyone to do some form of exercise every day. The difference between exercising before compared to after breakfast was much smaller than the difference between exercising at either time compared to not exercising at all."
The findings - in the research paper Effects of exercise before or after meal ingestion on fat balance and postprandial metabolism in overweight men - is published in the British Journal of Nutrition.