Energy is stored in our body in the form of carbohydrate, fat and protein. The body stores carbohydrate in the muscles and liver and uses this as our main source of energy. Once our carbohydrate stores begin to run low, the body starts to burn fat and eventually protein (muscles).
When we do vigorous exercise, such as long distance running or football training, our body uses the stored carbohydrate as the predominant energy source to enable us to carry on exercising.
If our diet lacks carbohydrate, then there won't be enough for the body to build up good stores. This affects our ability to sustain exercise and therefore worsens our performance as we will feel fatigued quicker. It also affects our ability to perform during shorter periods of intensive exercise such as weight training.
If your muscle carbohydrate stores are very low your body will switches to fat and protein breakdown for energy. However, this isn't a recommended form of exercise for losing fat, as you lose muscle as well.
Carbohydrate loading
High intensity, longer duration sports need high quantities of carbohydrate in the diet to build up carbohydrate stores, which help prevent early exhaustion and keep you exercising for longer and harder.
Carbohydrate loading is a technique used to increase the stores above normal levels, allowing you to exercise longer before fatigue sets in. Carbohydrate loading tends to be beneficial when taking part in exercise or sports lasting 90 minutes or longer.
There are many different regimes for carbohydrate loading but most use carbohydrate-rich foods varying in glycaemic index (the speed at which they are absorbed by the body) and recommend loading before, during, after and between exercise sessions.
Before exercise
It's recommended that you should eat a carbohydrate-based meal (pasta is a popular choice) 2-4 hours before training. This gives the food in your stomach a chance to settle before training and will leave you feeling neither too full nor too hungry during exercise.
During exercise
If you're exercising for less than an hour the only fluid you need to stay hydrated is water and, as long as you have good stores of carbohydrates pre-exercise (you're not following a low carbohydrate diet) then exercising for less than an hour shouldn't deplete your stores.
If you're exercising for over an hour, the carbohydrate stores in your muscles will start to deplete at a steady rate for up to 2-3 hours. At this point it will become very hard to carry on exercising at the same intensity, and you'll eventually feel fatigued and light-headed, the exercise will feel very hard and your muscles will feel very heavy. You'll eventually get to a point where you would stop exercising completely - known as ‘hitting the wall'. If you exercise for more than an hour (moderate intensity) then it's advisable to start consuming carbohydrate after 30 minutes to prevent getting to this point.
The type of carbohydrate you choose is up to you. It can be liquid (sports drinks, for example) or solid (sweets like jelly babies are popular) as long as you're also water to stay hydrated. Sometimes it's more practical to have liquid carbohydrates, which hydrate at the same time.
After exercise
After exercise it's very important to replenish your carbohydrate stores. The more depleted they are the longer it will take to replenish them. The higher the intensity or the longer the duration of the exercise, the more will have been taken from the stores. So, exercise such as running will use more energy than walking for the same period of time.
Similarly, the more carbohydrate you have after exercise, the quicker you will replenish your stores. This is particularly important if you train on a daily basis. Some research shows that if you consume some protein with carbohydrate after exercise, your carbohydrate stores will build up more efficiently, and the protein helps your muscles to recover as well.
It's best to start refuelling as soon as possible after exercise because the first two hours are the best time for carbohydrate to be stored quickly. The rate of storage slows down after that, and slows right down to normal levels after another four hours.
Between training sessions
It's still important after the six hour replenishment window to keep consuming steady amounts of carbohydrate. You can do this by eating small meals or carbohydrate-containing snacks throughout the day.
Alcohol
Drinking alcohol before training, even in small amounts, may make you feel more confident, but will impair your performance. Alcohol can reduce our reaction times, coordination, balance, strength, speed and endurance. It can also reduces the ability to regulate our body temperature, increases urination (potentially leading to dehydration) and reduces blood sugar levels, which can be dangerous.
Alcohol inhibits the body's ability to store carbohydrates, so a few drinks after a big win can prevent successful refuelling, regardless of how much carbohydrate you eat afterwards.
Finding the right diet for you
Practice your feeding strategy whilst you're training to understand what works best for you. Don't leave it until the day of the race or competition to try it out.