The Fat vs Carbohydrate Debate: Which one wins?

Metabolic testing results.

There’s a lot of debate about nutrition, especially when it comes to training and racing. There is no doubt that nutrition is the “fourth discipline” for Triathlon, but what is the correct approach? High carb or low carb, mediterranean, vegetarian, vegan, carnivore, gluten free, paleo… there’s a lot of options! 

The goal of this post is to simplify things a little bit. Let’s go back to the three macronutrients: fats, carbohydrates, and protein. 

• Fat has 9kcal (calories) of energy. 

• Carbohydrates have 4kcal of energy.

• Protein also has 4kcal of energy, but purely from an exercise standpoint if we have to dip into protein stores for energy, we’re probably already in trouble. 

To keep things really simple: 

• the aerobic system (slow twitch fibers) prefer to use fat as their fuel source. Fat is a very efficient source of energy but not incredibly powerful. At low intensities, we primarily burn fat for fuel and as the fiber name implies, go relatively slow.

• The anaerobic system (fast twitch fibers) prefer carbohydrate as their fuel source. Carbs are a very fast and powerful source of energy! Unfortunately, there are two problems. The first is that carbohydrate stores are limited, and taking in excessive amounts of carbohydrates is challenging on the gut (one of the biggest reasons for “bonking” in races is Gastrointestinal Distress). The second issue is that using carbohydrates means lactate is produced as a byproduct. Lactate is accompanied by hydrogen ions, which change the pH of the muscle tissue and is primarily responsible for the heavy fatigue feeling in the body at high intensities. So, carbohydrates help us go fast but at a higher cost.

The goal of any race is straightforward: get to the finish line as fast as you can. 

This means we want to combine the best of these two fuel sources! 
We can actually measure the amount of these that gets used at various intensities to see what is happening metabolically. 

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We know that most of us have roughly 2000kcal or 500g of glycogen (carbohydrate) stored in our bodies either in the liver or muscle tissue. This number can be up to 3000kcal / 600g with smart training and fueling strategies. We also know that most of us (even the skinny-mini’s) have close to 40,000kcal of fat stored! We’re not really at risk of running out of fat, but unless you train and fuel specifically, it can be hard to tap into. Even at low intesities, some people are only burning carbohydrates!

For our purposes, we can also take in carbohydrates in the forms of gel/liquid/solid etc. Everyone has their own thing, but I prefer SFuels and haven’t had any gut issues with it. It’s also helped my fat burning ability (more on that later). Focusing on the numbers, many of us can take in 60g of Carbohydrates per hour with little to no GI distress risk. Some of us can take in 90g. We’ll set these as the lower and upper limits, but remember we probably aren’t taking any in during the swim and getting fuel in on the run is astronomically harder than on the bike -> you’ll have to factor these into your own calculations!

With metabolic testing we can really pinpoint our racing and training plans by seeing how many grams of fat/carb we burn at different intensities. Below are some examples.

At goal ironman intensity (heart rate/power), generally speaking:

• Good fat burning is typically around using only 1g/Carb per minute.

• Medium fat burning is using 2g/Carb per minute.

• Bad fat burning is using 3g/Carb per minute.

So, let’s do some math!

GREAT FAT BURNING

MEDIUM FAT BURNING

BAD FAT BURNING

Once you find out your specific fat burn/carb burn rate, it’s a simple equation. I always like to have my athletes air on the side of caution because the swim/run intake rates are almost always lower and as much as I’d like to believe we all have another 100g of stored glycogen, it’s really hard to know that with certainty! 

Build up the fat burning with training the aerobic system and using the right fuel at the right time! I’ll go over this nutrition strategy more in depth at a later time, but the main focus should be on training at the right intensity and fueling for that specific intensity!

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Want to know your specific numbers? Come join our squad and do metabolic testing. We are here to help you raise your game. Best part - most of the time it means training EASIER! Contact Coach Griffin to get more into.