By Dr Mike Posthumus
ARE CARBOHYDRATES IMPORTANT?
When we are racing at high intensities, the predominant fuel used by our muscles is carbohydrates. Carbohydrates are stored in our muscles as glycogen. Our bodies are able to store roughly 500g of glycogen in our muscles and another 100g in our liver. However, this alone is not sufficient fuel to perform high intensity exercise for prolonged periods. When trained cyclists and runners (or any athletes) are performing at high intensities, their carbohydrate oxidation rates are normally in the range of 300g – 450g of carbohydrate per hour. Therefore, when we want to perform for prolonged durations, ingestion of carbohydrates is critically important.
HOW MUCH CARBOHYDRATE DO YOU NEED?
When trying to replace the fuel our bodies are burning in exercise, the primary issue is the rate of absorption of ingested carbohydrates. Early research established an upper limit of 60g of carbohydrates per hour. More recent research has shown that by including fructose in a sports drink in a 2:1 ratio (2 parts glucose and 1 part fructose) we are able to ingest 90g of carbohydrate per hour. This recommendation has recently been further increased to 120g per hour, once you have sufficiently trained your gut to be able to optimise the absorption of these sugars. The reason the composition of the sugars is very important is because glucose and fructose are absorbed through different channels. So if you want to optimise your fuel ingestion, choose a sports drink with one third fructose for optimal absorption rates.
Even at the upper limits of absorption (90g per hour), we are still in a very large deficit compared to what we are burning when we are cycling or running. Therefore when we are wanting to maintain performance for prolonged periods (well over 2 hours), we should aim to ingest 90g of carbohydrates each hour.
HOW DO YOU INGEST 90g CARBOHYDRATE / HOUR?
Your carbohydrate intake may come from either a liquid or solids, depending on your personal preference. You can reference the table below to see how many grams of carbohydrate are in some of Cadence Nutrition products. Every product on the market will include a full nutritional analysis, which does include these values.
Carbofuel Energy Drink (600ml) 55g
This should allow you to come up with your own nutrition plan before your next marathon race. For example, If you are planning on completing a marathon in 3 hours, you should plan and strategise to ensure that you have 270g of carbohydrates packed or available to you.
HOW DO I FUEL FOR MARATHON PERFORMANCE?
I personally like keeping it simple. If I am going to race for 4 hours, I always ensure that I have 4 (the number of hours) bottles (600g) of Carbofuel Energy Drink available. I would plan to finish a full bottle each hour. I would then pack 4 additional “snacks” – 2 bars and 2 gels. Then each hour I would either have a bar or a gel. This would equate to 86g per hour, which is close enough for me.
4 x Carbofuel Energy Drink (600ml) 220g
2x Carbofuel Energy Bar 80g
2x Classic Energy Gel 42g
Total 342g (or 86 g per hours)