Should You Exercise On an Empty Stomach?

 Jordan Siemens / Getty Images

Should you eat breakfast before exercising so you have some fuel in the tank? Or is it better to bust a sweat on an empty stomach? New research settles this debate, showing that skipping breakfast triggers beneficial changes in your fat tissue during exercise that don’t occur if you eat first.

To put both scenarios to the test, researchers from the University of Bath in England recruited 10 overweight but generally healthy guys in their twenties. One morning, the men ate a 600-calorie carbohydrate-heavy breakfast two hours before walking on a treadmill for 60 minutes at a moderate pace. Another day, after fasting since the night before, they did the same exercise with no food in their bellies. The researchers took samples of the participants’ blood and fat tissue before and after each treadmill test.

Skipping breakfast was the clear winner. In the fat tissue samples taken after the guys walked on empty stomachs, there was an increased expression of two specific genes. One gene suggests that the men’s fat stores had been tapped to rev metabolism, while the other indicates fat was used to fuel the exercise. “The direction of these changes in the genes imply that fat tissue is ‘healthier’ after fasted exercise,” says lead investigator Dylan Thompson.

By contrast, when the participants walked after eating a meal, these gene changes did not occur. “Feeding seems to blunt some of the responses to exercise in fat tissue,” Thompson says. “After eating, the adipose tissue is less involved in exercise. The body uses the consumed food to fuel the exercise, so there is no need for fat tissue to respond.”

Activating your fat stores in these ways can yield many positive health effects. “Our understanding of adipose tissue has changed enormously in recent years,” Thompson says. “We now know that it’s not just a passive store of energy. Instead, fat tissue plays a major role in health by secreting many different proteins that impact the heart, liver, muscles, and bones. So the overall health and function of adipose tissue is very important for many physiological systems.”