How to use the GI

So what does this mean for he cyclist who is aiming to keep their muscles well fuelled for enhanced performance?  This is an area that is creating a lot of interest in sports nutrition and most would agree that there is still a lot of work to be done.  However, based on current research, sports scientists have come to the following general conclusions on how GI could effect the athlete:

Before and event or training session

It is thought that a slow release, low GI carbohydrate meal before an exercise session of long duration may improve performance.  This is because the fuel is being released some time after the carbohydrate has been eaten.  This is most likely to be useful where a sustained release of fuel can’t be provided by intake during the session itself.

 If you want to try having a low GI meal before an event to see if it works for you, you may find that you are more comfortable during the session if you choose foods that are not very fibrous, bulky of gas producing.  Examples of these include pasta with a low fat sauce, some varieties of rice (eg. basmati) with stewed apple, porridge with skim milk, Sustagen Sport or tinned spaghetti on grain or barley bread.

We know though that the key factor is that you get enough carbohydrate pre-exercise.  Other factors to consider in addition to the GI will be taste preference, nutritional value, cost, practicality and gastric comfort.

During an event or training session

Carbohydrate taken during a long ride makes more glucose available to the muscles and brain so that you can exercise longer and with a clearer head.  Carbohydrates that are easily digested, absorbed and released into the blood stream would seem to be a good choice.  This means food with an intermediate to high GI.  Most sport drinks and popular exercise snacks fit into this category.  The exception is fructose (the carbohydrate in fruits), which are easily absorbed, but takes some time to be converted into glucose.  Hence it is used sparingly in sports drinks and would not supply your muscles quickly if you were to choose fruit juice to drink during a long ride.  Low GI foods are not usually taken during sport, except in ultra endurance events.

During the recovery phase after an event or training session

There is good evidence that intermediate to high GI foods accelerate the rate at which glycogen is replenished, compared to low GI foods.  (Carbohydrate is stored in the muscle and liver as glycogen, which is lots of glucose units stored together.)  this is particularly important if you have another event or training session in the same day.

In addition to sports drinks and some of the snack type foods already mentioned, you may like to try such things as potatoes, high GI cereals, jam sandwiches o creamed rice.  To kick start the recovery process, you need to have at least one gram of carbohydrate per kilogram of body weight within 30 minutes of finishing your ride.  Low GI foods such as lentils and legumes are probably less suitable for speedy glycogen replenishment and should not be the main source of carbs in recovery meals.

If you have 24 hours or more before you have to get on the bike again, it is more important that you eat enough carbs rather than being unduly concerned about the GI of your meals.

Different GI Combinations

There is another factor that needs to be considered in any discussion of the GI factor.  What you eat before and after exercise is likely to be a meal, not a single food.  The GI of the whole meal is the approximate average of the GI of the individual ingredients.  For example if you has baked beans (low GI) and white toast (high GI) you would have an intermediate GI meal.  The proportion of carbs from food will effect the overall GI.  This is however only and estimate, as we know, since other components in the meal can alter the GI, as can the way in which the meal is cooked and processed.

In Summary

The GI is a measure of how quickly carbohydrate foods are digested, absorbed and supply glucose to the bloodstream and working muscles.  It is not a measure of the nutritional quality of a carbohydrate rich food, but a factor that is useful to consider when choosing foods to fuel your sport.  It’s probably more important that cyclists eat enough great tasting carbs each day rather than focusing solely on the GI of foods and meals.

The GI is an area of active research.  Sports scientists may have to refine their advice once more studies are done.  If you would like to do more reading on the subject of the GI and how it may impact on your cycling performance, the following books are comprehensive without being difficult to read:

The GI Factor.  Brand-Miller et al, 3rd edition, Hodder and Stoughton, 1998.

The GI Factor – Pocket Guide to Sports Nutrition.  O’Conner et al, Hodder and Stoughton, 1997.

Click here to see Glycaemic Index Chart