3.2 Role of high GI foods for athletes
Foods with a high GI value have a useful role in the diet of athletes since they can be helpful in the speedy replacement of muscle glycogen stores. Table 1 shows examples of some high, moderate and low GI foods.
Table 1 Examples of high, moderate and low glycaemic index foods
|High GI||Moderate GI||Low GI|
|Glucose 100||Cornflakes 81||Potato (boiled) 56|
|Parsnips 97||Chips 75||Sweet potato 54|
|French baguette 95||Bagel 72||Bananas 52|
|Lucozade Original 95||Watermelon 72||White pasta 50|
|Honey 87||Wholemeal bread 71||Muesli 49|
|Potato (baked) 85||White bread 70||Porridge oats 49|
|Sports drinks 70||Baked beans 48|
|Weetabix 66||Apples 38|
|White rice 64||Yogurt 36|
|Shredded Wheat 64||Chickpeas 28|
|Raisins 64||Whole milk 27|
A summary of the key information about the use of the glycaemic index for physically active people is presented below:
- High GI foods are useful two to three hours before and during exercise and in recovery (within two hours of exercise) to speed up glucose entry into muscle cells and to replenish the glycogen stores quickly. Glycogen is replaced at its fastest rate within two hours of exercise.
- After exercising, glycogen stores need to be topped up quickly to be ready for the next training session. A high-carbohydrate diet with high GI foods immediately after training will result in greater glycogen storage. The term ‘bonking’ is used to describe the experience when cyclists become fatigued as blood glucose levels fall too low, although you may perhaps be more familiar with the term ‘hitting the wall’, often used to describe the same experience in long-distance running. Food or drinks containing high amounts of carbohydrate are the best choices for initial post-exercise snacks to replenish muscle glycogen stores in order to meet the demands of the next training session.
Assessing the effectiveness of your eating strategy
Keep a record of everything you eat and drink and all of the physical activity you undertake over a period of 2 or 3 days. Examine the times and frequency of your meals and drinks, and comment on their size. Also note the times and frequency of your bouts of exercise. How does your pattern of eating and drinking compare with the timings that would be most appropriate for exercise performance? Did you eat a high-carbohydrate snack within two hours of exercising? Judging the food record ‘by eye’, was your overall diet high in complex carbohydrate and low in fat?
Overall, a low-fat diet with plentiful low GI carbohydrates is desirable. Did you achieve this? To prepare for exercise, high-carbohydrate meals and snacks are needed to maximise stores. Both immediately before and during exercise that lasts more than one hour, carbohydrate foods with a high GI value will promote the storage of glucose as glycogen in the muscles. A high GI value post-exercise snack within two hours of exercise should be followed later by a low to moderate GI carbohydrate-based main meal. Were your snacks appropriate? Rehydration, both during and after exercise, is also important for recovery. Did you drink plenty of fluid at the appropriate times? If you are fully hydrated your urine will be a pale straw colour, no darker.