Anyone interested in sport is likely to have heard of the term 'carbohydrate loading'.  However it is probably one of the most misunderstood terms in sports nutrition. People commonly think anyone involved in sport needs to 'carb up' and the way to do this is to eat 'flat out' in the days leading up to an event.  Read on to get the facts on carbohydrate loading.

Carbohydrate loading is a strategy involving changes to training and nutrition that can maximise muscle glycogen (carbohydrate) stores prior to endurance competition.  The technique was originally developed in the the late 1960's and typically involved a 3-4 day 'depletion phase' and a 3-4 day 'loading phase'.  Ongoing research has allowed the method to be refined so that modern day carbohydrate loading is now more manageable for athletes.

Muscle glycogen levels are normally in the range of 100-120 mmol/kg ww (wet weight).  Carbohydrate loading enables muscle glycogen levels to be increased to around 150-200 mmol/kg ww.  This extra supply of carbohydrate has been demonstrated to  improve endurance exercise by allowing athletes to exercise at their optimal pace for a longer time.  It is estimated that carbohydrate loading can improve performance over a set distance by 2-3%.

Anyone exercising continuously for 90 minutes or longer is likely to benefit from carbohydrate loading.   Typically, sports such as cycling, marathon running, longer distance triathlon, cross-country skiing and endurance swimming benefit from carbohydrate loading.  Shorter term exercise is unlikely to benefit as the body's usual carbohydrate stores are adequate.   Carbohydrate loading is generally not practical to achieve in team sports where games are played every 3-4 days.  Although it might be argued that players in soccer and AFL have heavy demands on their muscle fuel stores, it would be impossible to achieve a full carbohydrate protocol within the weekly schedule of training and games.

Originally, carbohydrate loading involved a depletion phase.  This required 3-4 hard training days plus a low carbohydrate diet.  The depletion phase was thought to be necessary to stimulate the enzyme glycogen synthase.  The depletion phase was followed by a loading phase which involved 3-4 days of rest combined with a high carbohydrate diet.  The extra carbohydrate combined with the now-activated glycogen synthase was shown to boost carbohydrate stores beyond their usual resting levels.

Today's endurance athletes use a modified carbohydrate loading method.  Ongoing research has demonstrated that the depletion phase is no longer necessary.  This is a bonus for athletes as the depletion phase was very difficult.  Australian marathon runner, Steve Moneghetti has described the depletion phase as making him feel like "death warmed up".  Today, 3-4 days of exercise taper while following a high carbohydrate diet (7-10g/kg body weight) is sufficient to elevate muscle glycogen levels.

The following diet is suitable for a 70kg athlete aiming to carbohydrate load:

This sample carbohydrate loading meal plan provides roughly 14,200 kJ, 590 grams of carbohydrate, 125 grams of protein and 60 grams of fat.

Are there any special considerations for females?

Most studies of glycogen storage have been conducted on male athletes.  However, some studies suggest that females may be less responsive to carbohydrate loading, especially during the follicular phase of the menstrual cycle.  Further research needs to be conducted specifically on females. 

Research indicates that many athletes who attempt to carbohydrate load fail to achieve their goal.  The method sounds simple, so what are so many athletes doing wrong?  The most common mistakes are outlined below:

• Carbohydrate loading requires an exercise taper.  Athletes can find it difficult to back off and not train hard for 3-4 days before competition.  Failing to rest will compromise carbohydrate loading.
• Many athletes fail to eat enough carbohydrate.  It sounds easy to increase your carbohydrate intake but many athletes fall short of the mark.  It seems athletes don't have a good understanding of the amount of food required to carbohydrate load.  Working with a sports dietitian or using a carbohydrate counter can be useful.
• In order to consume the necessary amount of carbohydrate, it is necessary to cut back on fibre and make use of compact sources of carbohydrate such as sugar, cordial, soft drink, sports drink, jam, honey, jelly and tinned fruit.  Athletes who include too many high fibre foods in their carbohydrate loading menu may suffer stomach upset or find the food too bulky to consume.
• Carbohydrate loading will most likely cause body mass to increase by approximately 2kg.  This extra weight is due to extra muscle glycogen and water.  For some athletes, a fear of weight gain may prevent them from carbohydrate loading adequately.
• Athletes commonly use carbohydrate loading as an excuse to eat everything and anything in sight.  Consuming too many high fat foods will make it difficult to consume sufficient carbohydrate.  It may also result in gain of body fat.  It is important to stick to high- carbohydrate, low- fat foods while carbohydrate loading.

Carbohydrate counter of 50 g CHO portions from CHO-rich foods
(Adapted from Peak Performance: training and nutritional strategies for sport J. Hawley and L. Burke.  Sydney: Allen & Unwin, 1998.)
Each of the selections provide approximately 50 grams of carbohydrate:

Michelle Minehan, 2003

This is an archive copy of a document originally located at http://www.ais.org.au/nutrition/FactCLoad.htm
All copyright remains with the creator.

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