Total Athlete Coaching

Intermittent Fasting for Athletes


First Things First ...There are 2 fuel sources that your cells use for energy ...

Glucose and ketones. 

This article is not meant to debate the value of one over the other.

Quite to the contrary ...Instead, let's agree that there is value to BOTH as energy sources ...

This assumption is made on the idea that our bodies were designed (not mistakenly) to utilize both sources as fuel.

We also know that both of these fuels, when used for energy, create a completely different environment in your body and each environment serves our body in different ways. 

Let's take a look at a couple examples related to exercise ...


We know that with exercise, there comes cellular breakdown. In other words, damage is done.

Immediately upon completing an exercise session, cleanup and regeneration needs to begin. 

These two things happen simultaneously but a key point to understand is that each process is handled more efficiently and effectively in a particular physiological environment.

The physiological environment that is most beneficial for cleaning up the mess or "Taking out the trash" tends to be when ketones are abundant. 

The physiological environment that is most beneficial for rebuilding or "bringing in the groceries"  tends to favor an environment where there is an abundance of glucose for energy.

The key thing to takeaway from this example is BOTH environments offer some benefit to tissue healing.

Let's look at another example related to exercise.

Aerobic vs Anaerobic

There are advantages to the different environments created by the energy source in each type of exercise. 

Anaerobic exercise is optimized in an environment where glucose is the primary energy source. It's quick and easy to convert into energy and our bodies tend generally have large reservoirs in liver and muscle tissue.

Long duration aerobic exercise is optimized in an environment where ketones are used as the primary energy source. Because ketones are created though a breakdown of fat, we have huge resources available that can keep us going for many, many hours, and even days.

Ketones will fuel your cells long after glucose stores (glycogen) have been depleted.

Keeping these two examples in mind ...

We also know that our bodies are designed to be cyclical in nature. Consider something called circadian rhythms. These rhythms usually get referred to as the cycle between sleeping and waking, although; they are really tied to sun up or sun down.  

Both cycles are necessary for survival and each phase flips different switches on or off based on the cycle you are in. 

Sounds familiar, right?

So, how does this tie into Intermittent fasting and how can it benefit an athlete?

Intermittent fasting creates a swing of the pendulum from utilizing glucose as the primary energy source and then into ketones as an energy source. Ultimately, giving your body the opportunity to take advantage of the physiological environments created by both. It also allows your body to become more efficient in switching from environment to environment as needed.

Most Athletes (and the population at large), tend to stay in one physiological environment for most of their lives. As you can likely guess, we are extremely glucose dependent. 

This is due to 2 things ...

  1. A diet predominantly comprised of carbohydrates (easily converted to glucose for energy)
  2. Eating often - For many, we can spend 12+ hours a day in a fed state.

What you can do 

  • Cut down on Carbohydrate consumption ...especially the highly processed ones.
  • Intermittent Fasting - Decrease your feeding window. For example, only allocate 6-8 hours of time in your day where you can eat. The other 16-18 hours will be in a fasted state where your body gets a chance to swing the pendulum over to using ketones for energy.

Ultimately, this will create a balance of the systems at work by shifting back and forth between energy sources. 

A key thing to understand when playing with intermittent fasting is the time it takes for adaptation. 

If you have had been unrestricted eating for 12+ hours per day for as long as you can remember, it's going to be little uncomfortable for the first few weeks.  

Be patient 😉