Carbohydrate Loading

We’ve all been told to eat a large bowl of pasta the night before a race or training session. But why? Does it work? Are there better alternatives?

The first place to start is to understand the basics of carbohydrates.

There are two types:

Complex (or starches). These include grains and vegetables. Good Sources of starch are bread, cereals, porridge oats, potatoes, beans, lentils, rice, pasta, noodles.

Simple. These are sugars and sweets including fruit and dairy produce. Sugar is available in many forms:

• glucose - found naturally in fruit and vegetable juices
• fructose - occurs naturally in fruit and vegetables and especially in honey
• lactose and galactose - found in milk
• sucrose - occurs naturally in sugar cane and sugar beet
• maltose - available from fermented grain products

Carbohydrates should be the major energy providers in your diet. Current recommendations aimed at the entire population state that carbohydrate should provide a minimum of 50 percent of your total dietary energy (calories) with most of this coming from starchy carbohydrates.

Starch is a highly important nutrient in the diet and is the body's favourite "fuel". It is important because it provides most of our glucose, which is the only fuel the brain can use. In addition, starchy carbohydrates contain fibre and are very good at satisfying our appetites.

Carbohydrate and the athlete

A diet high in carbohydrates is particularly important for the athlete. We store very little glucose in the body so it is vital to have a regular intake of starch. This is because starch is converted to glycogen and stored in the liver and muscles. This glycogen is then used to meet muscles' energy needs by being converted back to glucose when the muscles exercise.

If the muscles run out of glucose they can also burn body fat, but fat is not as efficient an energy source as glucose. Therefore high levels of glycogen will help you exercise at your optimum level. On the other hand, low levels will result in early fatigue and reduced exercise intensity.

Your muscles can only store small amounts of glycogen, and they can't borrow glycogen stores from other areas. Normally, this isn't a problem. But if you start exercising at high intensity and continue for more than 60 to 90 minutes, your muscles will run out of glycogen, greatly affecting your stamina and performance.

So how can we make our muscles store more glycogen?

Well, carbohydrate loading is an option. It will gradually force your body into storing more glycogen. After an initial depletion stage, eating significantly more carbohydrates will fill your muscles with excess glycogen that can be used as fuel. This will delay the onset of fatigue. In addition to this, tapering your exercise a short while before an event will stop you using up your glycogen.

Should I carbohydrate load?

This is quite a good question. Carbohydrate loading is not necessarily for everyone. The best guide would be if you are doing a session or race that lasts more than 90 minutes then research suggests that “loading” might improve your overall performance. 

Short races (5km runs, short distance swimming etc) do not really need carbohydrate loading and would probably be wasted as your normal glycogen levels would be enough to fuel your muscles.

Things to watch out for:

Sadly, as with most things there is a down side to loading. It’s up to you to decide what's best for your event. Carbohydrate loading helps your body store extra water and so weight gain might be an issue. Also paying attention to high fibre foods before an event is advisable as it may cause discomfort, gas and/or cramps.

How much carbohydrate should you eat under normal circumstances?

Although the general recommendation for the population is that carbohydrates should supply a minimum of 50 percent of dietary energy (calories), it is probably important for athletes to increase this. Many sports nutrition experts suggest a minimum of 60 percent to 70 percent.

An easy method to work out how many calories from carbohydrate you should be consuming daily is:

If your total calorie intake is, say,	3,000 calories/day
then calories from carbohydrate	3,000 X 60 percent
	= 1800 calories

1 gram of carbohydrate = 4 calories, therefore, 1,800 calories is equivalent to 450 grams of carbohydrate.

Your total daily calorie intake from all sources should, of course, be linked to your body weight. In other words, you should be eating an amount that enables you to maintain your weight within its healthy range.

What about carbohydrate loading?

A suggested method for carbohydrate loading over a seven-day period prior to an event is as follows:- 

Day 1:  Endurance training for at least one hour to deplete your muscle glycogen stores.

Day 2,3,4: Taper off your training and eat a moderate carb diet. 5-7g per kg of body weight.

Day 5,6,7: Taper off training further and rest. While doing this have a high carb intake. 8-10g per kg of body weight.

You might want to experiment with this approach during training.

Carbohydrate intake while exercising

Glucose, itself, is not stored in the body. Once the available glucose in the blood stream and cells' plasma is used up, the body then turns to its supply of glycogen. As mentioned earlier, your body has limited stores of glycogen in muscles and liver ready for conversion to glucose. So, it is likely that for longer exercise sessions - say, more than an hour - you are going to deplete your supplies of glycogen and, therefore, run low on glucose.

Probably the best way to top up while actually exercising is with an isotonic sports drink as this will provide glucose, fluid and also sodium. An intake of between 30 grams to 60 grams of carbohydrate an hour is recommended. This is about the maximum your muscles can take up from the bloodstream during exercise. Greater amounts have no further benefit. It is best to start taking in carbohydrate soon after the exercise session begins because of the delay in absorption.

Carbohydrate intake after exercise

How long does it take to restore glycogen levels after exercise? This depends on how depleted your stores are after the exercise session, your fitness level, the amount of carbohydrate you eat and the extent of muscle damage.

It is best to replenish depleted stores of glycogen by taking in carbohydrate as soon as possible after your exercise session. During the first two hours, replenishment is most rapid and is approximately one and a half times the normal rate. During the following four hours, the rate slows down but remains higher than normal. Following this period, glycogen manufacture returns to the normal rate.

Restoring your glycogen levels as quickly as possible is very important, particularly if you train every day or every other day. This will help you avoid fatigue and get the best out of your training.

Key points

For athletes, carbs should provide 60/70 percent of total energy (calories). Most  of this coming from starch.          Simple sugar is not a good source of energy as it can upset the body's metabolism.          Starchy carbohydrates are the body's favourite fuel.          Glucose is the only fuel the brain can use and is the favourite for muscles.          Glucose is not stored in the body.          Glycogen, stored in the liver and muscles, is converted to glucose to provide energy for exercise.          Carbohydrate loading can help performance in endurance events.          Depleted muscle glycogen stores should be replaced as soon as possible after exercise (within 2 hours).

Adrian Lowther