Wednesday, 30 September 2015

The Science Behind "Carb Loading"

So, the big day is nearly here. You have trained for months and months and you can finally see a light at the end of the tunnel. But your final week is a very important one as you don’t want to ruin all the hard work leading up to the event.

If you’ve done your research, you will know that there are many things that can go wrong on race day. You could eat the wrong food and have an upset stomach. You could run out of stored glycogen and therefore run out of energy early on in your run. Or you could simply be dehydrated before you even begin the marathon. So, it’s no wonder that the preparation leading up to the marathon is just as important as the training itself.

One of the most common hurdles a marathon runner will face is hitting a wall during the race. The biggest cause of this is muscle glycogen depletion. Glycogen is a fuel derived from carbohydrates and is stored in the muscles and liver, before it is released into the bloodstream in the form or glucose.

The body will usually have enough glycogen to run for about 90 minutes. In order to reserve that much needed glycogen, experts suggest reducing the length and intensity of your runs in the week leading up to your race. This will enable your body to store the glycogen which would normally be used to fuel your longer runs. They also suggest pacing yourself throughout the marathon in order to burn through stored glycogen more slowly.

As mentioned above, glycogen is fuel derived from carbohydrates, hence why there is good reason to “carb load” about three to four days prior to the marathon. A high carb diet generally consists of 7-12g of carbs per kilo of body weight. During this period, try to avoid high fibre foods, gas producing foods and spicy foods as this may cause you to suffer from an upset stomach on race day.

During your “carb loading” period, you should expect to gain roughly 2 kilos due to the extra muscle glycogen and water in the system. Think of it as the extra “fuel” your body will be carrying to help you complete those gruelling 42.2 kilometres. But don’t worry, your normal weight will resume once the marathon is over.

Of course, while increasing your carbohydrate intake, it is best to avoid the high fat foods such as chips, pastries, donuts and the like and concentrate on white rice, pasta with a tomato sauce, oats and english muffins just to name a few. Experts also suggest, as with any dietary changes, that you try out the “carb loading” method prior to the actual marathon.

Protein intake should be between 1.2-1.8g per kilo per day. For example, a 70kg athlete would need to eat between 84-126g of protein per day. Protein is essential for not only muscle repair and recovery, but when combined with carbohydrates, it can help improve protein balance and absorption.

So what does a high carbohydrate diet look like? The following diet is an example provided by the Australian Sports Commission ( and is suitable for a 70kg athlete:

3 cups of low-fibre breakfast cereal with 11/2 cups of reduced fat milk
1 medium banana
250ml orange juice
toasted muffin with honey
500ml sports drink
2 sandwiches (4 slices of bread) with filling as desired
200g tub of low-fat fruit yoghurt
375ml can of soft drink
banana smoothie made with low-fat milk, banana and honey
cereal bar
1 cup of pasta sauce with 2 cups of cooked pasta
3 slices of garlic bread
2 glasses of cordial
Late Snack
toasted muffin and jam
500ml sports drink*

This sample plan provides ~ 14,800 kJ, 630 g carbohydrate, 125 g protein and 60 g fat.

It is also important to eat a meal at least two hours prior to a marathon to allow the food to be digested. If nerves are a problem for you, try having a liquid breakfast like a smoothie if that is easier to stomach. You will need the energy from this meal to help with your glycogen levels.

Hydration is also key in the lead up to the marathon. Be sure to drink plenty of water during the days prior to the race to ensure you start out hydrated. A pee test is the best way to measure this. If your pee isn’t a light straw colour, then you need to drink more until it is. Dehydration places a huge strain on the body and can significantly affect your running performance. Make sure you start drinking water or sports drinks* early on in the race to minimise the risk of dehydration.

Sports drinks* are a great way to replace lost electrolytes. Sweat consists of three electrolytes; sodium, chloride and potassium, with sodium having the greatest concentrate. Therefore you may benefit from extra sodium. Be sure to practise your hydration strategy prior to the marathon.

After completing the marathon, it is equally as important to refuel, repair and rehydrate your body. After a long run, you have a window of approximately 30 mins when your body is primed to replenish its carbohydrate stores and soak up muscle-repairing protein. A glass of milk, a protein shake* or a smoothie provides a good mix of protein and carbs. Drinking plenty of fluids is also important to replace the water and electrolytes lost through sweat.

So to sum up, ensure you have a nutrition plan, a hydration plan and a “carb loading” plan in place and tested before the marathon so you know exactly what to expect. You don’t want to be dealing with any nasty surprises on the morning of the marathon. Be sure to have a meal at least two hours prior to the run and don’t forget to refuel, repair and replenish post marathon.
Author: Hayley Polsen
*for information relating to a range of protein shakes and electrolyte drinks specifically designed for athletes, please contact the author of this article

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