An Introduction to Carbohydrate Consumption for Cycling

Carbohydrates are one of the three macronutrients we consume in our food. Normally referred to as carbs or sugar/sugars, this family of molecules is made up of carbon, hydrogen, and oxygen and generally form chains. These long linking molecules can be any variety of lengths, with the shortest being glucose (which is actually a ring) and some of the longest being glycogen, a molecule produced in the body from glucose. The good news is: you don’t need a chemistry degree to understand carbs well enough to fuel your workouts with them. So let’s take a look at how carbs fit into a cyclist’s diet.

Carbs for Athletes

If you have a look the three energy systems humans can use to produce energy, two of them use exclusively carbs for their energy substrate, and the third, the Aerobic system, uses more and more carbs as the intensity increases. The truth of the matter is any moderate or high intensity exercise uses carbs as the main source of energy. Without carbs the Anaerobic system is unusable and the Aerobic system is massively diminished, not to mention the lightheadedness from no sugar flowing into your brain! For any athlete, not just endurance athletes, other than the longest of events (8+ hours) require carbs for performance beyond low-moderate intensity. Anything beyond a light jog starts to incur carb utilization.

So what does that mean? EAT CARBS! The fueling demands of cyclists are high, with high total energy output, there is a need for high energy input. A cyclist should consume some 60-70-80% of their energy from carbs, especially during periods of high total exercise load. Eating enough carbs can be tough, especially because they do not go down as easily as fat and protein. Carb ingestion and absorption are also more complicated than first meets the eye. If you shove down a bunch of carbs all at once, how much is stored to prepare for your next workout? Actually, less than you think.

Glycogen is the main method of storing carbs in the body. Simpler carbs such as glucose and fructose among others, are absorbed into the liver and muscles where they are converted to long-chained carbs, called glycogen. A normal human has the capacity to store about 500g of glycogen in the body. This process occurs slowly with a steady-state rate of around 30-40g of glycogen per hour. The goal of ingesting carbs after working out is to provide the body with the substrate it needs to produce more glycogen. This glycogen is then used to fuel your next workout. If we start a workout with full glycogen levels, there is a much better chance we can finish all of our intervals. Professional cyclists ensure their glycogen stores are full before their workouts and so should you.

As I said before, it’s not as easy as just eating sugar all day. Since the body slowly produces more glycogen throughout the day, our goal is to slowly provide carbs to our body throughout the day. If we were to eat a giant milkshake, undoubtedly it would contain plenty of carbs, some 100g+, but our body doesn’t have the capacity to process all that sugar at once. So, instead our body shuttles the sugar out of our blood and attempts to convert it into fat for storage, or we get a sugar rush and burn through it in order to reduce our blood sugar levels. Chronic excessive sugar in the blood is associated with metabolic disorders such as diabetes. The correct protocol then, is to eat a moderate amount of carbohydrates throughout the day to find the correct balance between providing enough carbs to refill glycogen stores and not eating so much that our blood sugar levels are too high.

This balance is difficult, but can be made easier by a few things. For one, eating complex carbs such at oatmeal, brown rice, and al dente pasta can slow down the rate of absorption of carbs and dampen the spike in blood sugar. It has also been shown that eating fat and fiber can reduce the rate of absorption of carbs. A diet high in complex carbs, some healthy fat, and fiber is an effective way to maintain moderate blood sugar levels, perfect for glycogen synthesis.

The commonly cited protocol for replenishing glycogen stores is 0.5g carbs per kg body weight per hour. Or for most of us, something like 35-40g per hour. I tend to use the easier conversion of 1g/kg/2hrs which for me is approximately 70g of carbs per two hours. Remember, this protocol is intended for replenishing glycogen stores, which max out at about 500g. So these stores are full after some 12-14 hours of 0.5g/kg/hr and all consumed carbohydrates above that level go to fat storage or instantaneous use by the body. If there is no need to replenish glycogen stores for the following day’s workout (i.e. a rest day), then there is no reason to follow this protocol. A standard diet is sufficient to replace glycogen stores over a two or more day period.

Post-workout Recovery

Every recovery drink brand will swear you NEED to have carbs after your workout. It is true that glycogen synthesis rates increase by 3x directly after a workout, but it is not necessary to ingest carbs directly after a workout. As long as you continue to eat carbs throughout the day, it’s likely your glycogen stores will be full before your next workout. The reason to eat carbs after a workout is to lessen the load of glycogen synthesis and take advantage of the increased glycogen synthesis rate. If you can ingest some 75g of carbs, most commonly simple sugar, that sugar will all go into your glycogen stores. This can be advantageous if you need to do another event later in the day or don’t have access to carbs throughout the day, such as in some work situations. Taking a recovery drink after a workout for glycogen synthesis is a bit of a take it or leave it, just make sure those stores are full before your next workout.

Conclusion

Carbs are by far the most important macronutrient for endurance athletes. Ensuring carb stores are full is essential to getting the most out of you workout and maximizing training stimulus. The keys here are:

  • don’t eat too much simple sugar, look for complex carb sources
  • eat carbs with a bit of fat and some fiber to slow down the absorption rate
  • ensure carb ingestion is spread out to give the body time to synthesize glycogen
  • ensure sufficient carbs are ingested to maximize glycogen stores
  • hydrate – glycogen synthesis requires a lot of water

Keeping to these principles can help ensure your energy is topped off and you get the most out of your workouts.

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