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Between Carb Dependency and Keto there's a place called Metabolic Flexibility - I'll Meet You There

Jill here - performance nutrition is the art and science of fueling exercise and recovery.

Note the art and science piece. Science is full of competing ideas. The art is figuring out what works for you in your discipline or distance.

So let's get on the same page with some basics.

Adenosine tri-phosphate (ATP) is the chemical energy that fuels movement and performance, in fact fuels all body processes. It causes muscle fibres to contract and produce force. We can't store nor can we eat ATP in appreciable amounts so our cells are constantly producing it and breaking it down to release chemical energy. When you exercise, the demand for ATP goes up significantly and rapidly.

The two primary substances our bodies use to produce ATP are carbohydrate (in the form of glucose) and fat (in the form of fatty acids). Our cells make moment to moment decisions on what proportion of carbohydrate and fat to use depending on a number of different and complex factors. Think heart rate, availability of oxygen, exercise duration, outside environment, endogenous levels of hormones and enzymes, etc.

One factor, however, that has a profound effect is the immediate availability of carbohydrate. The more carbohydrate that is available, the more carbohydrate versus fat will be used to produce ATP.

This is why you might believe that carbohydrate is the preferred fuel source and you pack gels and banana's in your back pockets.

Don't mistake preferred fuel source as a better fuel source though. Depending mostly on carbohydrate for ATP production in performance can be a fickle business. A carb dependent athlete is more likely to bonk than a more metabolically flexible one.

Conversely when carbohydrate is low a greater proportion of fat is used to produce ATP. Folks who advocate the ketogenic diet do make a lot of good points. For sure, our body fat provides an incredible reserve of fuel which becomes vitally important the further you go and it's a welcome thing for most athletes not to have to constantly manage carbohydrate intake.

A true ketogenic diet however usually limits carbohydrate to under 50-75grams per day to maintain the correct hormonal environment to adequately access fat. Calories are maintained through a high fat diet (usually 85% of calories).

Many folks find this challenging. Again, depending on one fuel source can be fickle business.

I prefer the middle ground especially for you endurance athletes. You want to be able to seamlessly alter the ratio of how much fat versus carbohydrate is used to produce ATP depending on your environment. Metabolic flexibility brings options.

If you want to increase the ratio in favour of using more fat to meet the demand for ATP, think about decreasing carbohydrate, even by 15-30g per hour. Especially think about restricting fast acting carbohydrates because they do have a lasting impact on your ability to shift the ratio back in favour of using fat. Ditch the gels and the high sugar bars for more complex carbohydrates and foods higher in fat. The Meridian Peanut Cocoa bar is just one great example.

We are innately built to have great flexibility in how we meet performance ATP demands.

Let's learn to use it wisely.

More blogs to come on some great topics like eTRF or early time restricted feeding and intermittent fasting. All useful tools in the quest to turn your body fat into chemical energy!


If you're interested in learning more about performance nutrition pop on over to our performance coaching section. If you're interested in endurance racing check out the Team Joe Barr 200 and The Joe Barr 500 at

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