Does morning exercise burn more fat?

Will I burn more fat if I don't eat before exercising?

Yes and no.

Exercising first thing in the morning before eating is referred to as fasted cardio and is often promoted among individuals looking to lose weight. The idea behind it is that when you are sleeping at night, your organs deplete the carbohydrate stores in your liver. If you then exercise before giving your body any new carbohydrates, your body is forced to utilize fat as a fuel source. So, in the short term (i.e. over the course of your workout), you will indeed burn more calories from fat than you would if you were to eat a source of carbohydrate prior to exercising.

In the longer term, however, that perceived benefit has consequences. When carbohydrate stores in your liver become low it triggers the release of cortisol, a stress hormone. The release of cortisol is what promotes greater utilization of fat stores for fuel. The release of cortisol also has two other main effects, however:

  • In addition to promoting greater fat utilization, the release of cortisol also promotes the use of protein in your body for fuel. This essentially means that your body is burning muscle tissue to support your exercise. If your goal is to build muscle during exercise, exercising in a fasted state is not doing you any favours.
  • The release of cortisol is your body’s way of conserving carbohydrate stores in your liver when they start to get low. Cortisol also promotes conservation in other ways as it has a suppressing effect on your metabolism. This has short term effects, such as less energy during your workout, and longer term effects, such as fewer calories used over the course of the rest of the day after your workout.

The bottom line?

Fasted cardio represents a very narrow approach to health and well-being. While exercising in a fasted state does mean that you will burn slightly more calories from fat during your workout, it also prevents you from pushing hard during your workout and results in loss of muscle mass and suppressed metabolism in the longer term. These side effects far outweigh any perceived beneficial effects that fasted cardio may have.

Fasted cardio also represents a narrow approach to health and well-being as it promotes the use of exercise for the sole purpose of fat loss. Exercise can have many physical and mental health benefits including improved heart and brain health, improved energy, reduced stress, and better sleep. If fat loss or burning calories are your only motivators for exercise or if you strongly associate health with the number on the scale, however, there may be cause for concern. 

So then, what should I eat before a morning workout?

Aim to include a small amount of carbohydrate and protein prior to working out to give your body the fuel it needs without upsetting digestion during exercise. Great examples could include:

  • A banana with a 1 cup of milk or soy milk
  • Fruit and ½ cup of yogurt
  • A slice of toast with nut butter
  • A handful of cereal with ½ cup yogurt
  • Make a smoothie with a banana, berries, 1 cup milk and ½ cup of yogurt. Drink ½ before your workout and save the other ½ to have as part of your breakfast.

Questions about your diet and nutrition needs? All University of Guelph students have access to Student Wellness Services nutrition services (free and fee-based options are available). Students can access these services in three ways: