Fasting can be defined as the abstention of eating during a certain period of time. Which can sound a little scary when we are constantly surrounded by food in this world. Even worse when you think about jumping on a bike or going out for a run with no food. Am I going to bonk out ? You need to realize that we actually fast every night, it is a natural physiological process necessary for a healthy performing metabolism.
HOW DOES A FASTED TRAINING SESSION WORK ?
It is a training session done on an empty stomach ( a minimum of 6 hours with no food) at low intensity. This allows for glycogen stores to be fully depleted and means that the body has stopped breaking down food. In theory, this would facilitate increased fat burning by lowering insulin levels and depleting glycogen stores enough that body fat would be broken down and burned as free fatty acids for fuel.
DO YOU BURN MORE FAT DURING A FASTED EXERCISE ?
As I said, when you fast, insulin levels drop almost instantly, allowing body fat to be broken apart and burned as free fatty acids. Glycogen stores also become depleted, meaning that less or no glucose is available for energy during exercise. In theory, fat becomes the body’s new fuel.
In practice, it’s more complicated than that. The percentage of fat burned depends on the intensity of the exercise.
low-intensity aerobic exercise (walking, light jogging, easy bike ride,... ) while fasted appears to enhance fat-burning.
moderate or intense exercise while fasted doesn’t increase fat burning. Oxidation is roughly the same in both the fuelled and fasted state. (Because high-intensity aerobic exercise releases more fat into circulation than you can possibly need)
It is important to remember that fasted training enhances fat-burning during light exercise, but not during more demanding sessions.
SO WHAT ARE THE POTENTIAL BENEFITS OF TRAINING FASTED ?
Enhanced fat utilization: only valid on low intensity sessions.
Better endurance: fasted cardio leads to an increase, over time, in VO2 max—a measure of endurance capacity.
More growth hormone: Both fasting and exercise increase human growth hormone (HGH) to better redistribute energy in the body.
Ketosis: Improve blood sugar levels.
WHAT SHOULD I EAT AFTER A FASTED TRAINING SESSION ?
A meal or a snack rich in protein ( rich in leucine) and carbohydrates.
Protein shake with an apple
Scrambled egg & avocado toast
Oatmeal/Granola with milk
Berry yogurt bowl
Chicken and rice
Salmon and sweet potato
Peanut butter and banana toast
THE BOTTOM LINE
Fasted training should be monitored. Depending on your goals, you could include fasted training into your training load. Keeping it low intensity is the key.
Marine LENEHAN, sports nutritionist, yoga teacher & massage therapist
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