Exercising on empty burns more fat?

Posted: April 12, 2011 in Nutrition, Training
Question: Should You Exercise on an Empty Stomach?
If I exercise on an empty stomach in the morning, will I burn more fat?
Answer: The theory behind this is that your blood sugar levels are low when you’re in a fasted state (after going all night without eating) which targets more fat burning.

The problem is that just because you’re using more fat as fuel doesn’t mean you’re actually burning more fat off your body. Burning fat is more about overall calorie expenditure, not just about the type of energy your body is using for your workout. Another problem is that you may not be able to workout as long or as hard if you’re hungry, which means you may end up burning fewer calories than if you’d eaten something and worked harder.

There are other benefits to eating before your workout:

  • It can boost recovery and strength gains
  • It can help you sustain longer, more intense workouts
  • It can help you avoid low blood sugar, which can make you feel dizzy or nauseous
  • It can make your workouts more enjoyable (since you’re not thinking about eating the whole time)

The bottom line is, we each have to find a system that works for us. You may be fine doing cardio without a meal in the morning, but strength training may require more fuel to really challenge your muscles. The best answer to this is to do what works for you. Don’t go hungry just because you think you’re burning more fat…after all, if you cut it short or lower the intensity because of low energy, how much fat are you burning anyway?

A study published in 1999 in the journal Medicine and Science in Sports and Exercise had a group of people ride an exercise bike on two mornings: on one day after a small breakfast, and the other after eating nothing. The researchers found that when the subjects ate nothing, they became fatigued faster and stopped exercising about 30 minutes earlier.

Dr. David Prince, an assistant professor of rehabilitation medicine at the Albert Einstein College of Medicine of Yeshiva University in New York, said that when you exercise on an empty tank, your body burns through stored carbohydrates first, then protein, before it finally moves on to fat. In the meantime, he said, “you lower your blood sugar, causing ravenous hunger that in most people would lead them to eat much more than they would otherwise.”

If you do eat before a workout, make sure you give your body time to digest. The larger the meal, the more time you’ll need. But, if you choose a light snack (100-200 calories) and stick with higher carb fare, you can probably exercise after about 30-60 minutes. Pre-workout snack ideas:

  • Banana (or other type of fruit)
  • Yogurt
  • Oatmeal
  • Energy bar or gel
  • Fruit smoothie
  • Sports drink


THE BOTTOM LINE: Exercising on an empty stomach burns a higher percentage of fat but shortens your workout and makes them less intense due to fatigue, resulting in a lower total caloric expenditure necessary for weight loss.





Kirwan J, O’Gorman D, Evans W. A moderate glycemic meal before endurance exercise can enhance performance. 1998. J Appl Physiol 84: 53-59.


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