Glycaemic Index

The glycaemic index (GI) refers to the rate at which the carbohydrate in food is digested and absorbed by the body. Foods are ranked on a scale from 0 - 100 according to how much they raise glucose levels in the blood after eating a standard amount of carbohydrate.

Many factors determine the glycaemic response of a particular food, including:

  • the amount of carbohydrate consumed
  • type of carbohydrate (such as amylose starch or amylopectin starch)
  • type of fibre
  • presence of protein and fat in the food
  • food form (for example, flour can be finely milled or stone-ground)
  • the amount of processing the food has undergone.

A low-GI carbohydrate is one that is digested and absorbed slowly by the body. That is, a low GI food results in a relatively gradual rise and fall in blood glucose levels.

Low-GI carbohydrates help maintain steady blood sugar levels. They also help sustain energy levels throughout the day and avoid fluctuations between extreme highs and lows.

In sports and exercise, choosing carbohydrate foods based on their GI may assist performance.

Low-GI carbohydrate before exercise help provide slow and sustained energy release to muscles throughout the event. This is particularly important for events lasting longer than 90 minutes, such as tennis, some fun runs and football.

Low-GI foods can be more filling and may help control your appetite so that you don't overeat.

In general, most unprocessed (natural), whole foods have a low GI.

Some low-GI foods include:

  • Milk and yogurt
  • Wholegrain bread
  • Legumes
  • Temperate climate fruits such as apples and pears.

On the other hand, high-GI carbohydrate foods are broken down quickly during digestion. These foods cause a rapid rise and fall in blood glucose levels. Most processed, refined foods (such as white sugar and white rice) have a high GI.

High-GI foods cause blood sugar levels to rise quickly, delivering energy more rapidly and are ideal to quickly top up carbohydrate stores during sports which involve short, sharp bursts of activity, such as netball, sprinting and soccer.

High-GI foods are also useful to aid recovery after exercise, particularly if you have training sessions every day or are playing in a round-robin competition.

Examples of high-GI foods are:

  • White bread
  • Potatoes
  • Low-fibre breakfast cereals.

Now go to Energy-dense vs Nutrient-rich Foods.