Completing the London Marathon is a major achievement for many, whether this be in a fast time or simply completing the distance. To succeed requires a considerable amount of training and motivation. There are certain nutritional aspects that need to be taken into account: hydration and energy.
Although there are cases of runners overheating the typical climatic conditions for the London marathon should not pose major hydration problems, so providing the athlete starts the run fully hydrated and takes the opportunity to consume further fluids at feeding stations dehydration should not be a problem.
Providing sufficient energy to complete the run is another matter. The human body primarily provided energy for long duration exercise from carbohydrates and fats stored in the body. Even for thin people their fat supplies are considerable, it is the carbohydrate that causes the problem. There is a phrase that “fat burns in a carbohydrate flame”. This means that to be able to metabolise fat and to produce energy the body needs to be metabolising carbohydrate. Many people who have run a marathon will be familiar with the phrase “hitting the wall”, typically around the 20 mile mark. This coincides with the point when carbohydrate levels fall so low that the ability to produce energy becomes compromised and the runner slows down dramatically.
A good analogy here is the fuel in the tank of a car. A car with a full tank, driven at an economical speed will go further than a car being driven fast. This is because the higher speed uses the fuel more rapidly. This works the same for the marathon runner. The well-paced runner reaches the finish line with an empty tank and the fastest possible time.
Elite runners, through years of training have developed a very efficient energy production system and a huge fuel tank. Their muscles adapt to the miles of training by being able to store more glycogen (the storage form of carbohydrate) and also they have an ability to produce more energy from fat and also from protein. This enables them to “spare” their glycogen. Thereby achieving phenomenal times such as Dennis Kimetto’s 2 hr 2min 57 sec in the Berlin marathon in September 2014.
Elite runners will also have a diet that is high in carbohydrate. The typical western diet has about 50% of its calories coming from carbohydrate. Elite endurance athletes are recommended to have at least 60% and perhaps up to 75% of their energy coming from carbohydrate. Typically the western diet contains about 200-250 grams of carbohydrate per day but the endurance athlete would be eating double that quantity or more. 7-12 grams of carbohydrate per kilogram of their body weight per day is the amount recommended by leading authorities. So for a 70 kg person this would be 490-840g of carbohydrate. Bearing in mind a portion of rice (62g uncooked) provides 47g of carbohydrate, this can represent quite a bit of food.
Recreational marathon runners (if that is not a contradiction in terms) do not have the benefit of long term adaptations created in response to years of training but there are things that can be done to the diet that can help.
When marathon running became a popular activity and a challenge that people sought to achieve research into nutritional aspects of running began to be published. A key realisation was that running time was significantly related to initial muscle glycogen levels and glycogen levels could be affected by dietary intake. This led to the creation of the carbohydrate loading diet in the 1970s. The classic carbohydrate loading diet involved a run to exhaustion seven days before the event. Followed by three days on a diet high in fats and protein but low in carbohydrate. This effectively starved the body of carbohydrate and made it crave carbohydrate when it became available. The runner would then eat a diet very high in carbohydrate and the body would store much greater quantities of glycogen. A rebound effect occurred. This led to the famous “pasta parties” the night before a marathon and runners tried to top off their stores of valuable carbohydrate.
The problem with this approach was that exhausting run and the low carbohydrate days. Runners were very lethargic, exhausted and not well prepared mentally for the up and coming run. It was realised that a less drastic approach was also quite effective. In the days leading up to the marathon the runner should taper their training and increase their carbohydrate consumption. This also leads to increased muscle glycogen levels.
In simple terms, to help with either completing the run or running faster, people should increase their carbohydrate consumption by eating greater than normal quantities of rice, pasta, potatoes and other carbohydrate rich foods and taper their training.
A key feature for success is always pace judgement. The faster you go the faster you will deplete your glycogen stores.
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Senior Lecturer, Sport & Exercise
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