The carbohydrate sweet spot for ultra-endurance cyclists

To fuel successfully over ultra distance can be a challenge both for nutritionists who coach ultra-cyclists, and for the riders who specialise in ultra-endurance cycling.

We all know that the further you go, the more complicated it gets!

One of the first things to do, is to find your happy carbohydrate place within your fuelling system.

This is both an art and a science.

The science, when it comes to carbohydrate, is full of competing ideas – from high carbohydrate to low carbohydrate, to multi-forms of carbohydrate – you can find an expert or evidence to support that point of view.

The art is figuring out what works (and keeps working) for each rider over distance.

A little ultra-endurance nutrition science

Adenosine tri-phosphate anyone?

Adenosine tri-phosphate (ATP) is the chemical energy that your muscle cells use to fuel your performance.

Muscle fibres need it to contract and produce force, from your heart beating, to your hip flexors, flexing.

We can’t store it, nor can we eat it in appreciable amounts, so our cells have to constantly produce it, and then break it’s bonds to release energy.

When you train or race, the demand for ATP increases significantly and rapidly.

When you race over great distances, day and night, the demand reaches unimaginable levels.

Carbohydrate availability

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, or more specifically, the mitochondria within our cells, make moment to moment decisions on what proportion of carbohydrate and fat to use depending on a number of different factors – heart rate, availability of oxygen, trained state of the athlete, outside environment, and so forth.

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

This is why carbohydrate is considered the preferred fuel source, and why most cyclists pack gels and bananas in back pockets.

Don’t mistake ‘preferred’ fuel source as a ‘singular’ fuel source though.

Depending mostly on carbohydrate for ATP production in ultra-endurance can be a fickle business. A carbohydrate dependent ultra-cyclist is more likely to run into gut issues, given the amount of carbohydrate per hour needed to sustain performance.

Most guts can handle high amounts of carbohydrate over 6-8 hours but after that, undigested and unabsorbed carbohydrate can cause a multitude of issues, collectively known as ‘sloshy gut’.

And if carbohydrate availability decreases (you run out of fuel), you can bet your back wheel that a bonk is on your horizon.

Low carbohydrate availability

Conversely, when carbohydrate availability is low, a greater proportion of fat is used to produce ATP.

Folks who advocate a very low carbohydrate diet or ketogenic diet do make some good points.

Body fat provides an unlimited reserve of fuel. Plus it spares the need for constant carbohydrate fuelling, making managing gut comfort a whole lot easier.

A true ketogenic diet, however, limits carbohydrate to under 25-50 grams per day.

That may be great for body composition but can be extremely limiting when it comes to competitive performance as efficient fat oxidation occurs under specific conditions – lower heart rates and high oxygen availability.

Unless you are a highly efficient ultra-athlete, this often translates to a slower speed.

Once again, an over-dependence on one fuel source can be fickle business.

A little ultra-endurance nutrition art

This ultra-endurance nutritionist prefers the middle ground.

The middle ground where the ratio of ATP production from fat versus carbohydrate is managed by balancing factors like fuel availability, fuel type, terrain demand and environmental costs (think heat, cold, windy or altitude).

This requires metabolic fitness and flexibility, and like all things performance it needs trained.

Alan Couzens, an ultra-coach and exercise physiologist puts it this way,

“Your typical metabolically unfit individual is burning 100 cals of fat per hour, i.e. one pound of fat every 35 hours.

A metabolically fit athlete can burn six times this. They can burn a pound of fat every 5-6 hours.

If you want to lose body fat, it’s important to have a high ability to use fat as fuel.”

Building metabolic fitness

It is possible to train your metabolic fitness (thus increasing your rate of fat oxidation) by decreasing carbohydrate intake to roughly 0.3-0.5g per kilogram per hour while holding a heart rate with good oxygen availability.

This will likely be zone 1-2, depending on your starting point.

I would especially restrict large amounts of fast acting carbohydrates (like the 25-30g in most gels). Instead I would favour small, consistent sips of carbohydrate through bottle mix with additional small amounts of solid food.

Consistency is key when training metabolic fitness. Your goal is to provide a specific amount of carbohydrate per hour, every hour, while holding a steady pace.

The perfect time to train your metabolic fitness is in the winter months when your focus is on building base milage. Those long, low heart rate, miles add up, as will your metabolic fitness.

Of course, when you start to intersperse your training with high intensity sessions, it’s best to fuel those accordingly.

One last thing…

There’s lots more we can do to support metabolic fitness, both on and off the bike.

Your metabolism is a responsive system. It responds to inputs when it comes to food choice, timing and volume.

You need to stay vigilant around those inputs if you want your metabolism to ‘stay fit’, and flexible.

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I work with athletes who want to hone their metabolic fitness, and non-athletes who want to develop metabolic fitness and flexibility.

There are numerous ways to work with me. Check out what people have said.