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Carbohydrate Loading

What is Carbohydrate Loading?

Carbohydrate loading or carbo-loading is a term used to describe a nutrition technique used by endurance athletes in an attempt to prolong optimal athletic performance and delay the onset of fatigue, or, ‘hitting a wall’.

The Transformation of Food into Energy

When we eat carbohydrate-containing foods, they arrive at our stomach and begin to break down. From the stomach, the partially broken down food travels to the small intestine where it completely breaks down into many compounds, one being glucose. From the small intestine, the glucose is absorbed into the bloodstream. A hormone called insulin which is secreted by our pancreas accompanies the glucose from the blood to our liver and muscle cells, where it is stored in the form of glycogen. From this stored form, the body can transform glycogen back into glucose through a process known as glycolysis, and use it for energy when needed.

When is Carbohydrate Loading Appropriate?

Carbohydrate loading has been shown to only be beneficial for athletes competing in endurance events lasting longer than 90min. This includes events like marathon running and triathlons.

The reason carbohydrate loading is indicated only for endurance events lasting more than 90min is due to the body stressing its aerobic energy system and depleting all of its stored energy. What do I mean by this? Our body naturally reserves some energy in the form of glycogen for daily activity and these stores can last us a modest duration of light-moderate intensity activity e.g. netball game, tennis game, a run or a jog.

As exercise intensity increases, so do the rate of glycolysis in the liver. i.e. as the intensity of the exercise increases, the rate at which glycogen from the liver is broken down into glucose to be used as energy also increases. This glucose is transported to the muscles where together with muscle glycogen, it is utilised for energy.

However, when the body is active for 90 minutes or longer, those energy stores from our regular diet begin to exhaust and the body turns to other, less efficient energy supplies like fat. So, in order to maintain optimal athletic performance and delay the onset of fatigue, endurance athletes engage in carbohydrate loading.

How to Do It

Carbohydrate loading strategiesPreviously, the most popular carbohydrate loading strategy involved vigorous exercise and little carbohydrate intake so as to deplete all glycogen stores for a few days leading up to the event. Then one day prior to the event, zero exercise and high carbohydrate intake so as to saturate liver and muscle glycogen stores.

The most recent research into techniques of carbohydrate loading is as follows:
Three days prior to the event, the athlete must increase his/her carbohydrate intake to 5-12g/kg body weight per day in order to saturate glycogen stores to around 150-200% of their normal levels.

This is a pretty wide-range due to a variety of factors. For example, one study showed that increasing from 10g/kg/day to 13g/kg/day increased muscle glycogen stores further, but did not result in improvement.

Important factors to consider are how much carbohydrate people can tolerate without GI, in addition to the increase in water weight associated with storing more glycogen (approximately 3-4g water per 1g of glycogen stored), which might not be desirable under some circumstances.

Secondly, during these days, training must decrease, to avoid burning through this glycogen. Thirdly, the day before the competition, the athlete ideally should completely rest in order to ensure minimal energy expenditure, and hence maximal glycogen storage.

Do’s and Don’ts

It is important to note that different meal plans can have differing effects on the body. For this reason, it is imperative that the athlete trial foods prior to the event, to ensure no unforeseen gastrointestinal disturbances during the event.

High fibre foods like grain bread, wholemeal pasta and brown rice, without an adequate fluid intake, can cause gastrointestinal upset including constipation, flatulence and bloating which are all very uncomfortable sensations, particularly during vigorous exercise.

In order to maximise carbohydrate intake whilst not overdoing your fibre intake, one should try to avoid increasing fibre intake to beyond their typical intake. To achieve this, it is ideal to focus on including low-fibre carbohydrate sources such as white bread, white pasta, white rice, juice, milk, yoghurt and other options.

However, gastrointestinal upset is not uniform amongst all athletes. Not everybody will need to be focusing on lower fibre sources.

Another really important thing to be aware of is that when people “carb load” on their own without a plan, they often do not consume enough carbohydrates to optimise performance.

For example, they might typically consume 3g/kg/day and increase that to 5g/kg/day, which is on the low end of the recommendations but might not be enough to maximise performance.

One reason why people fall into this trap is that they might be consuming higher fat carbohydrate sources, or choosing higher fibre sources and getting full too quickly, or just lacking awareness of how much is actually required. It is highly recommended to have some form of plan in place and ensure that the plan contains sufficient carbohydrate to implement a proper carbohydrate load.

An Extra Top Up

Another way of topping up on energy during an event is to drink sports drinks like Gatorade or Powerade. They not only supply instant energy in the form of simple carbohydrates, but they also hydrate and replenish electrolyte losses. Below is a table comparing the nutritional value of a range of sports drinks.

  Gatorade Gatorade Endurance Powerade Powerade Zero Maximus Staminade
Energy 103kJ 108kJ 129kJ 6.8kJ 130kJ 106kJ
Protein 0g 0g 0g 0.05g <1g 0g
Fat – total

       Saturated

0g

0g

0g

0g

0g

0g

0g

0.1g

<1g

<1g

0g

0g

Carbohydrate

– sucrose

– glucose

6.0g

5.5g

0.5g

6.2g

5.7g

0.5g

7.3g

5.7g

1.6g

0.1g

0g

n/a

7.4g

6.0g

1.6g

6.0g

4.4g

1.6g

Sodium 51mg 84mg 28mg 51mg 30mg 37.9mg
Potassium 22.5mg 39.2mg 14.1mg n/a 30mg 18.6mg
Magnesium n/a 1.4mg n/a n/a 4mg 2.9mg
Calcium n/a 2.7mg n/a n/a 2mg

Remember, carbohydrate loading is only useful for events which demand it. For short duration events, this technique will be useless as these activities do not demand the body to utilise extensive glycogen stores.

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