THE RATE OF DIGESTION

The GI factor is a ranking of foods from 0 to 100 (see Glycemic Index Range) that tells us how fast a food will raise our blood glucose (sugar) levels. For example glucose has a glycemic index of 100 whereas fructose (sugar from fruit) is only 23. Yes, not all sugars are equal either. What really surprised scientists, was that many starches (bread, potatoes, rice) are digested and absorbed quickly. Baked potatoes for example have a GI factor of 85.

Nutritionists point out that the key is the rate of digestion. Carbohydrate foods that are digested quickly have the highest GI factors. Conversely, those that break down slowly have low GI factors. Mixing different carbohydrate foods in a meal will have the effect of averaging the GI.

Thus foods with a low GI will have less effect on your blood sugar or glucose than foods with a high GI. High-GI foods tend to cause spikes in your blood glucose levels, which means you will probably feel peaks in your energy levels but you are also likely to come crashing down! Low-GI foods, on the other hand, tend to cause gentle rises in blood sugar and less of a rush or drop in energy levels.

Glycemic Index range

(Glucose is used as the standard or reference food with a GI of 100)

Low-GI foods: below 55
Intermediate-GI foods: 55 to 70
High-GI foods: more than 70

THE GI AND SPORTS PERFORMANCE

One of the more important applications of the GI to sports performance is in recovery nutrition. A diet high in carbohydrates is a must for optimum performance. Carbohydrate is stored in the muscle as glycogen. An athlete needs to make sure these stores are well-maintained to prevent fatigue when exercising.

After exercise, these stores need to be replenished. Research has shown that high-GI foods consumed immediately after exercise speed up the recovery of muscle glycogen. This is because high GI carbohydrates increase blood glucose quickly and stimulate more insulin - the hormone responsible for storing glucose as glycogen.

An athlete who does not completely replenish glycogen stores after a training session, will fatigue more quickly in the following training session.

Fifty to 100g (or 1g per kg of body weight) of high-GI food is required immediately after exercise. Examples of suitable foods are - white bread, rice, cornflakes, jelly beans and electrolyte sports drinks.

Other applications of the GI in sports nutrition are before and during exercise. Research has found that a low-GI pre-exercise meal may enhance endurance in long workouts while high-GI foods or fluids during exercise help maintain blood sugar levels.