Updated 13 December 2019

Carbo-loading considered

Serious athletes use carbohydrates to fine-tune their performance by means of carbo-loading. DietDoc explains the process.

Serious athletes who train strenuously for many hours a day and participate in premier sporting events use carbohydrates to fine-tune their performance. Fine-tuning is achieved by means of a process called carbo-loading.

Glycogen is a compound used by the body to store carbohydrate or readily available fuel in the liver and muscles. These carbohydrate stores are not extensive and are easily depleted if the athlete does not replenish them thoroughly before an event.

Carbo-loading is undertaken to prevent the following:

  • too rapid depletion of glycogen stores in the liver and muscles;
  • development of hypoglycaemia (low blood sugar levels) during exercise.

The above-mentioned factors can cause fatigue and poor performance. It is, therefore, in the best interest of any serious athlete to ensure that his or her glycogen stores are optimally filled before an event.

Carbo-loading before an event
a) Non-endurance events

Events that last for 60 to 90 minutes can be classed as non-endurance events. According to Burke and Deakin (2000), an athlete can normalise his glycogen stores by resting for a period of 24 hours and ingesting between 7 and 10 g of carbohydrate per kg of body weight per day.

An athlete weighing 70 kg would need to eat 490 to 700 g of carbohydrate for at least 1 to 1,5 days before a non-endurance event to refuel his glycogen stores adequately. This is a large amount of carbohydrate to ingest and many athletes fail to meet this recommendation.

In some cases athletes, particularly female athletes, are unwilling to increase their food intake to such levels because they fear that they will gain weight. To achieve maximum performance, it is essential that dietary restrictions are postponed and the athlete carbo-loads for 1 to 1,5 days before an event.

Carbo-loading is usually combined with a reduction in practice intensity for the 1 to 1,5 days before an event, something some athletes find hard to understand or do. The reason for this ‘rest period’ is to ensure that the carbohydrate the athlete ingests, is stored as glycogen and not used during the pre-event training sessions.

b) Endurance events
When athletes compete for periods exceeding 90 minutes (marathons, triathlon, cycling etc.), carbo-loading is even more essential and should last about three days in the period before the event. Once again, the increased carbohydrate intake of 7 to 10 g of carbohydrate per kg body weight per day should be accompanied by a reduction in training intensity.

Research has shown that carbo-loading can postpone the onset of fatigue, extend the period of maximum exercise capacity by as much as 20%, and cause an increase of 2 to 3% in performance (Burke & Deakin, 2000). These are desirable goals for top athletes who need a steady supply of fuel for the intensive work their muscles have to do for extended periods.

Carbo-loading and female athletes
Female athletes who compete in endurance events may not respond to carbo-loading as effectively as male athletes. Research studies are still trying to determine why this occurs, although there is some evidence that the menstrual cycle may play a role.

Preliminary results indicate that women store glycogen more efficiently during the luteal phase (the second 14 days) of their menstrual cycles, than during the follicular phase (the first 14 days of the cycle).

However, the finding that female athletes may store glycogen less effectively in response to carbo-loading could also be due to the fact that they are more inclined to eat a low-carbohydrate, low-energy diet throughout their training period than male athletes because they fear weight gain.

Despite these problems, female athletes will also benefit from carbo-loading if correctly applied.

Does carbo-loading cause weight gain?
The answer to this question is ‘Yes’ and that a gain in weight of about 2 kg is an indication that the carbo-loading programme is working effectively. Elite athletes will lose these 2 kg and more weight during strenuous events, so the gain in weight should not be regarded as a negative effect, but rather as proof that the athlete is refuelling his glycogen stores properly.

This concept may be difficult to handle and many athletes, especially female athletes, may need to change their perceptions to accommodate this recommendation. If you do gain weight when carbo-loading, don’t stress about it, because you will lose this weight during the event.

Need for guidance
Athletes may find that they react negatively to carbo-loading with carbohydrate foods that contain a great amount of dietary fibre or roughage (wholewheat, or unsifted or unprocessed grains and cereals), which may cause abdominal distress, cramps, diarrhoea and winds in sensitive individuals.

To prevent such problems the athlete should firstly consult a clinical dietician to help her work out a carbo-loading regimen that does not cause fibre reactions and pre-test such regimens during periods when the athlete is not competing seriously.

Low-fibre carbohydrates which may be useful for carbo-loading include white bread, sifted maize meal, standard breakfast cereals (not fibre-enriched), white rice, plain pasta, canned or peeled fruit (also remove pips and seeds), instant oats and noodles, carbohydrate-rich drinks (cold drinks, fruit juices) and carbohydrate supplements.

When is carbo-loading not required?
Carbo-loading is generally not required under the following circumstances:

  • Non-endurance events that do not last longer than 60 minutes
  • High-intensity events that last only a few minutes (sprints, short-distance running)
  • If the athlete is already using a very high carbohydrate diet on a constant basis (e.g. marathon runners or Tour de France cyclists who eat as much as 800 g of carbohydrate per day)
  • Athletes with health problems such as poorly controlled diabetes or raised blood fat levels, especially high triglyceride levels

Carbo-loading is, therefore, a tool that serious athletes of both genders should consider and apply before important events. Because these high-carbohydrate regimens may be difficult to understand, apply and sustain, assistance from a clinical dietician can make the difference between the success and failure of both your carbo-loading programme and your actual sports performance. – (Dr I.V. van Heerden, DietDoc)

Any questions? Ask DietDoc


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