Nutrition: Carbohydrates 101

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Wednesday, 02 August 2006  |  Written by Shelly Meltzer and Cecily Fuller (courtesy of Fast Fuel)

Critical for Optimal Performance 

No matter what your sport, carbohydrate is the critical fuel for optimal performance. Exercising muscles rely on carbohydrate as the main source of fuel. Therefore diets low in carbohydrate can lead to a lack of energy during exercise, early fatigue, loss of concentration and delayed recovery. All carbohydrates, once digested, are eventually converted into blood glucose or stored as glycogen in the liver and muscle for later use. Excess carbohydrate will be stored as fat.

Since the 1920s scientific studies have revealed the ergogenic properties of carbohydrates. Later studies showed that a relatively high carbohydrate intake appears to delay the onset of fatigue during endurance type events. This refers to pre-event carbo-loading of 600–700g/day to maximize liver and muscle glycogen stores. Similarly, carbohydrate ingestion during exercise also delays the onset of fatigue by sparing liver glycogen, but the mechanisms of this effect seem to be governed by central regulatory functions rather than solely as a consequence of delaying an impending ‘energy crisis’.

There is also evidence that in high-intensity, intermittent exercise lasting less than one hour, carbohydrate loading and carbohydrate ingestion during exercise (30-60g/hr) appear to impart some neuro-protection from fatigue.

In summary, all the evidence shows that carbohydrates have an important role before, during and after exercise. This may vary between individuals and the mechanisms are not completely understood. Ingesting carbohydrate during exercise is the most effective way of preventing hypoglycaemia (low blood sugar levels).

Stores
The total amount of carbohydrate that your body can store as glycogen in the liver and muscle is minimal (about 600g) compared to your body’s fat stores. Liver glycogen stores are use to top up the glucose levels in the blood to ensure that the brain maintains its essential glucose supply. Regular training rapidly depletes these small reserves and you therefore need to ensure an adequate daily carbohydrate intake. Decreasing glycogen stores can cause your body to start breaking down muscle protein for much-needed glucose. This will have unfavourable consequences, one of which is the loss of lean muscle mass, and therefore strength.

Carbohydrate-rich foods include grains, cereals, dairy produce, fruit, certain vegetables, sports-specific products and sugar. The amount you need depends on your training programme and other dietary goals. Your training requirements will be in the range of 5-7g/kg body weight, with a maximum of 600-700g per day (60% of energy intake, or more). However, this may vary depending on your daily energy expenditure, type of sport, gender and environment. In situations involving either extremely prolonged and intense exercise or repeated bouts within an 8-12 hour period, requirements may increase to 8-10g/kg body weight. In extreme sports such as Tour de France, this may be as high as 12g/kg body weight.

50g carbohydrates:
Grains
3 thick slices bread
10 crackers or 6 rice cakes
2 cups high-fibre (bran) cereal
3 breakfast wheat biscuits
2 cups porridge
1 cup pasta or 1 heaped cup rice
1 cup samp/polenta/couscous
3 medium bran muffins
2-3 muesli or breakfast bars

Vegetables & Legumes
1 cup baked beans
3.3 cups peas/carrots/butternut or mixed vegetables
3 medium potatoes or 1 cup sweet potato

Fruit
3 medium pieces of fruit (apple/banana)
40ml raisins
2 cups fruit juice

Dairy
1 litre skim- or low-fat milk or buttermilk
1.5 cups low-fat, flavoured drinking yoghurtor 1 cup fruit yoghurt

Carboloading
For endurance events (all events lasting longer than 90 minutes) you need to maximize your muscle glycogen stores:

• Three days before the event (when your training should be tapered), consume 8-10g carbohydrate/kg body weight. For a 50kg athlete this means consuming 400-500g carbohydrate per day and for a 70kg athlete 560-700g carbohydrate per day.
• Carbohydrate must form the bulk of all meals and snacks.
• Fluids and concentrated sources of carbohydrate can be used to ensure you meet your target.
• Over the last 24 hours you can reduce the fibre and bulk of the diet to ‘race light’.
• 2-3 hours before the event have a light pre-event meal.

Sample carbohydrate-loading eating plan:

This material is an extract from ‘Eating for Sport’, published by Struik and available through leading bookstores. Shelly Meltzer, who has an MSc (Med) Nutrition and Dietetics, heads the dietetic practice associated with the Sports Science Institute of South Africa. Cecily Fulleris a registered dietitian with a BSc (Med) (Hons) in Sports Science.

PS from the Editor: Fast fuel's Ultimate Carb is an excellent way to increase your daily carbohydrate intake. It can be added to foods, drinks, etc as it is a flavourless product. It is a 98% pure carbohydrate supplement with no unnatural additives.

Article reproduced with kind permission of Fast Fuel