Sports nutritionist Hannah Sheridan considers the history of carbohydrate loading and how it is best implemented

So what exactly is carbo-loading and why should you do it? The process is a short-term strategy involving a change in training and nutrition with the aim of maximising muscle glycogen (carbohydrate) stores prior to endurance competition lasting 90 minutes or more.

Muscle glycogen is the dominant and most efficient energy source used during the majority of exercise events that we participate in. However, it is a limited source of energy that becomes depleted after approximately 90 minutes of moderate intensity exercise. Therefore, by maximising our carbohydrate stores through a carbo-loading protocol, we are able to continue to exercise at the same given intensity, for a longer duration. Evidence suggests that performance is improved by 2-3%, which over the marathon distance would equate to a considerable time improvement.

When?

Carbo-loading one to four days prior to endurance events lasting longer than 90 minutes can aid performance in endurance running, cross-country skiing, swimming, cycling and triathlon events. In shorter events, carbohydrate stores are adequate to support performance so carbo-loading is not necessary.

Some will argue that the performance of high-level team sport athletes, such as footballers, may benefit from carbo-loading. However, the training and competition schedule within these sports does not allow for a taper period, making the carbo-loading practice impossible to be of any use to performance.

How?

Since the 1960s when the carbo-loading strategy first emerged, the protocol has varied dramatically. Today the procedure is much less severe, more user friendly” and also highly effective. Originally, it was thought that six to eight days was required to complete a successful carbo-loading.

This involved a three to four-day depletion phase in which carbohydrate stores were drained through high-intensity training and maintained by following a severely low carbohydrate diet. This was followed by a three to four-day loading phase incorporating rest and a high-carbohydrate diet in order to maximise muscle glycogen stores.

This often left athletes feeling extremely fatigued, susceptible to illness and in a negative mindset when it came to the start of their event. Steve Moneghetti, the Commonwealth marathon gold medallist in 1994, summarised it as being like death warmed up!”

The current, most effective carbo-loading protocol can be carried out just one to four days prior to competition. Carbohydrate stores have shown to be fully restored after 24 hours of rest combined with a high-carbohydrate diet. Therefore, today s procedure does not require a high intensity training period or carbohydrate restricted phase, but instead an exercise taper in conjunction with a high-carbohydrate diet (8-12g/kg of bodyweight).

For many, this will simply mean continuing with your usual high carbohydrate diet, but ensuring that training volume is reduced considerably.

It is wise to remember though that carbo-loading is not one single large pasta meal at the marathon pasta party! It involves an exercise taper, if not complete rest, combined with a high-carbohydrate diet during the week (one to four days prior) leading up to the event.

Tips for carbo-loading

Ensure that you consume low-fibre, easily digested carbohydrate sources to reduce the risk of gastro-intestinal distress and bloating such as fruit and vegetables (with the skin and seeds removed), white bread, white pasta, white rice, honey, jelly and refined cereals such as cornflakes

Do not think of it as an opportunity to eat as much as you can or over-consume junk food. This will compromise your intake of valuable nutrients required to help continual recovery, support immune function and provide you with the right sources of energy prior to race day

Remember that muscle glycogen is stored with water, so you can increase body mass by up to 2kg during this period

Daily intake example
60kg athlete

Carbohydrate intake: 9g/kg of body mass
Breakfast: 120g of low-fibre breakfast cereal with 250ml of milk, one banana, 250ml orange juice
Snack: Toasted fruit teacake with honey
Lunch: Two sandwiches (white bread) with lean meat or tuna filling, 200g low fat fruit yogurt
Snack: Banana smoothie with honey and milk
Dinner: One cup of pasta sauce with two cups of pasta, vegetables and lean meat, two slices of garlic bread, one glass of cordial
Late snack: Two slices of toast with jam

Hannah Sheridan BSc, PGDip, MSc, is the lead sports nutritionist at the University of Birmingham high performance centre, where she supports national and international-level athletes competing across a range of sports

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