You may already know not to eat a meal before going to the gym.
But scientists have confirmed the tale – and claim that the biggest gains may happen on a completely empty stomach.
Working out while hungry may even be beneficial to someone’s health in the long-term, the first study of its kind suggests.
After eating, the body is too busy responding to the meal consumed to focus on burning calories.
This means exercising straight after eating won’t help to shift any excess pounds in the form of adipose tissue – mainly responsible for obesity.
Instead, the body uses the consumed carbohydrates as its energy source – not the desired form fat people want to shift.
However, going to the gym while in a fasted state may help to burn the fat and even turn it into muscle, researchers believe.
Study author Dylan Thompson, of the University of Bath, said that adipose tissue often faces competing challenges.
After eating, adipose tissue ‘is busy responding to the meal and a bout of exercise at this time will not stimulate the same [beneficial] changes in adipose tissue’.
He added: ‘This means that exercise in a fasted state might provoke more favourable changes in adipose tissue, and this could be beneficial for health in the long term.’
For the study, published in the American Journal of Physiology – Endocrinology and Metabolism, the researchers studied a group of overweight males.
They walked for 60 minutes on an empty stomach, and for the same time frame two hours after having a carbohydrate-heavy breakfast.
Multiple blood and adipose tissue samples were taken after eating or fasting, as well as before and following the exercise.
They discovered that the gene expression in the adipose tissue differed significantly in the two trials.
Both PDK4 and HSL increased when the men fasted and exercised. However, they decreased in the men who had eaten before walking.
The rise in the former likely indicates that stored fat was used to fuel metabolism during exercise instead of carbohydrates from the recent meal.
The increase in the latter usually occurs when adipose tissue uses stored energy to support increased activity.
This comes after University of Surrey researchers found a way for men and women to be able to burn more fat without doing extra exercise.
In their study last January, they said changing the timing of when each gender eats could burn up to 22 per cent more fat.
However, as with so many thing in life, they found the secret was vastly different between men and women.
While men burned more fat if they exercised before eating, it was the opposite for women.