Is it better to exercise on an empty stomach? Many fitness gurus recommend working out without eating – first thing in the morning – to burn more fat. Needless to say, it’s a challenge to crawl out of bed at the crack of dawn and hop on the treadmill without so much as a cup of orange juice. Does exercising on an empty stomach really burn more fat?
Working Out without Eating: Does It Increase Fat Burning?
It’s true that exercising before eating in the morning breaks down more fat, but the amount of additional fat that’s lost isn’t as great as most people think. If you’ve gone eight hours without eating, you’ve depleted most of your glycogen stores. As a result, you force your body to use fat as fuel. On the other hand, the amount of additional fat burned exercising before eating isn’t enormous – despite what the fitness gurus say.
Exercising on an Empty Stomach: Why It’s Not Such a Good Idea
Working out before eating comes at a price. When your glycogen stores are depleted, and you work out at a higher intensity – you’ll have to stop sooner. This is because type 2 muscle fibers do much of the work during high-intensity exercise, and they use almost exclusively carbohydrates as fuel. If glycogen stores are depleted, you won’t be able to exercise as hard or as long as usual. This is why athletes carb-load before competing, so they can give their strongest performance.
Some people who exercise hard before eating may experience symptoms of low blood sugar. The lightheadedness, dizziness, and fatigue that go along with hypoglycemia make exercise more difficult – or even dangerous. People who take insulin for diabetes should never exercise without eating first.
Working Out without Eating Could Break Down Muscle
If you do a long or intense workout without replacing glycogen stores after an overnight fast, you run the risk of breaking down muscle. When the body is fuel deprived, muscle tissue is broken down, so the liver can use the protein to make glucose through a process called gluconeogenesis. This supplies energy both to hardworking muscles as well as the brain. Unfortunately, most people don’t want to lose lean body mass along with the fat.
Should You Exercise on an Empty Stomach?
It’s probably not a good idea to exercise before eating. The amount of additional fat you’ll burn is small, and you may be forced to stop early from fatigue, which means you’ll burn fewer calories overall. You also run the risk of fatigue, weakness, and loss of lean body mass. If you exercise before eating, do it for thirty minutes or less – and be sure to refuel afterward.
Exercise Physiology. McGraw Hill. Powers and Howley. 2009.