Fast to Burn fat?
Ellen Coleman, RD, MA, MPH © 2004

If I want to increase my body's fat burning ability, should I skip breakfast and drink only water on workouts?

Ah, the "I burn more fat by not eating" myth. The short answer is no, exercising while fasting does not increase fat metabolism. Fat may contribute slightly more to the fuel mixture while fasting. However, regular exercise is beneficial for weight loss because it helps to create a calorie deficit. The fuel being burned to create this calorie deficit (fat or carbohydrate) is probably not important.

I'm going to make several comments about breakfast, exercise refueling and also about fat burning:

The main goal of breakfast is to ensure adequate blood glucose levels for the workout. After an overnight fast, liver glycogen (the source of blood glucose) is about 80% gone. Working out on empty for 45 to 60 minutes at a moderate intensity is unlikely to harm performance.

However, no breakfast may hamper performance during a long, hard workout (over an hour) workout that requires a ready supply of blood glucose.

The key to increasing fat metabolism is through endurance training, not skipping breakfast. Aerobic exercise starts the fat burning process via increases in fat burning hormones (epinephrine, norepinephrine, and growth hormone) and decreased insulin release. This hormonal milieu favors fat metabolism and occurs whether or not one has eaten breakfast.

Chronic endurance training increases fat metabolism by increasing the number and size of mitochondria (which contain the enzymes necessary to burn fat) and increasing capillary density (greater delivery of blood and oxygen which is necessary to burn fat).

For a competitive athlete, it is generally counterproductive to exercise on empty. Skipping breakfast also does not increase fat metabolism – that occurs as a benefit/adaptation of endurance training.

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