Is it true that … you burn more fat by working out on an empty stomach? | Diets and dieting

‘There’s a bit of truth,” says Javier Gonzalez, professor of nutrition and metabolism at the University of Bath. “When we exercise, we always burn a mixture of fuels, mainly carbohydrates and fats. If you fasted overnight, you’ll typically burn a little more fat and fewer carbs than if you ate breakfast, especially a high-carb breakfast. But that doesn’t mean fasted workouts are better for weight loss.

“We can only store a small amount of carbohydrates as glycogen in our muscles and liver. Any extra energy – from carbohydrates, fats or proteins – is ultimately stored as body fat. So to lose fat, you have to be in an energy deficit: burning more energy than you consume. If that’s not the case, it doesn’t matter whether you’re fasted or fed – your body balances things out over time,” says Gonzalez.

However, this does not make training on an empty stomach useless. Research, including Gonzalez’s, suggests that training in a fasted state can slightly improve metabolic health, particularly how muscles adapt to exercise and how the body handles spikes in blood sugar, which can lead to energy crashes. “Training in a fasted state appears to encourage the muscles to remove glucose from the bloodstream,” he says. “So this can improve blood sugar control, especially after meals.”

The effects are most visible during endurance exercises such as jogging or cycling. During higher intensity exercises, such as sprint intervals, the body relies heavily on carbohydrates in all cases. Overall, the benefits of training in a fasted state are modest.

“The most important thing is to do the exercise. Whether you do it fasted or fed is just the icing on the cake,” says Gonzalez. If you want to try it, start small – 15 or 20 minutes – and gradually increase. “If you feel dizzy or dizzy, that’s the signal to stop and eat something.”