The body can only hold about only 18 miles-worth of easily useable energy. But unless you top up your fuel reserves on the run, it starts trying to conserve that energy after as little as 9 miles, which will affect your performance. When your body senses that your easily accessible reserves of carbohydrate energy have fallen to 40 or 50 per cent, it starts to increase its use of fat as a source of fuel.
It simply cannot let your blood sugar reserves empty completely, because your brain relies on them. The trouble is, fat can’t be turned into energy nearly as fast as blood sugar can, so your body becomes forced either to slow down, or to increase its effort dramatically to maintain the same speed (in both cases, you’ll find yourself breathing more heavily, because fat conversion requires more oxygen).
The simple solution is to take in fuel on any run over 80 or 90 minutes (and also fluid on any run over an hour, in normal conditions). Energy drinks can meet both your fuel and fluid needs, but if you have access to water on your run (e.g. race drinks stations, park water fountains, corner shops and garages!), gels are more practical.
Essentially, they’re concentrated drinks of about 100 calories each, so nearly all require you to drink water in order to create a digestible solution in your stomach. Exactly which gel to use is a matter of personal preference. There are a number of gels on the market, and many are an acquired taste.
Take a look at reviews of some of the main brands.
If you don’t fancy gels, other food options include bananas, jelly babies and jelly beans – all containing simple sugars and easily digested by the body, though the energy you receive from them will last for less time than gels or energy bars. Two important things to remember: experiment with different options on your training runs to see what your stomach likes best, and don’t try anything new on race day.
In terms of hydration, there is plenty of evidence to suggest that sports drinks do offer an advantage over plain water whilst training and racing. Sports drinks are useful during in marathons because they replenish your blood sugar and slow down the depletion of your glycogen stores. If you plan to use sports drinks on race day then you need to make it part of your training regime.
Read more about marathon training nutrition and hydration at the Runners World site or on the Real Buzz marathon site.