Glycaemic index: how quickly does the blood sugar level rise?

Definition

The glycaemic index was developed as a measurement tool in the 1980s during diabetes research. GI (as it is shortened) shows how quickly the blood sugar level rises after eating foods containing carbohydrates. The values are given in percent and refer to the consumption of 50 g of carbohydrates. The index uses the effect of pure glucose as its reference value.

The glycaemic index is generally divided into three categories:

1. Over 70% is high GI
2. Between 55-70% is medium GI
3. Under 55% is low GI
   

Glycaemic index: what's important at a glance

• The higher the glycaemic index, the faster a food causes the blood sugar level to rise and the more insulin the body has to release in response.
• Strong fluctuations have many negative effects, including hunger attacks.
• If these highs and lows persist, the effect of insulin can wear off and diabetes can develop.
• People who have frequent hunger attacks, are overweight or at risk of developing diabetes should therefore focus more on low-GI foods.
• By contrast, endurance athletes taking part in competitions need fast-working energy that goes directly into the bloodstream, so they will choose high-GI foods.
  

A small example: glucose is a simple sugar that doesn't need to be split and goes directly into the bloodstream. By comparison, the carbohydrates in whole-grain products are long chains of simple sugars and the body needs time to break them down.

The glycaemic load

One look at the table immediately shows that white bread and watermelon have a similarly high GI. This suggests that watermelon causes the blood sugar level to rise rapidly. The catch is: GI is calculated per 50 g of carbohydrates, not per food. This means that in practice you would have to eat about 800 g of watermelon to reach 50 g of carbohydrates. Almost impossible without exploding.

Scientists also recognised this problem and therefore developed what is known as the «glycaemic load». This provides information about the quality of the carbohydrates and the amount eaten. The glycaemic load of watermelon is only 6 compared to white bread at 34, and is therefore healthier.

How applicable is the glycaemic index?

In everyday life, GI is not very applicable:

• The combination of foods plays a major role. This is because fats, proteins and fibre can slow down the rise in blood sugar levels. For example, sugar enters the bloodstream much more slowly when combined with proteins.
• The glycaemic index fluctuates depending on ripeness and preparation.
• Depending on age, hormonal factors, muscle mass and levels of everyday activity, the release of insulin varies from person to person.
  

Our conclusion

The glycaemic index can be used as a guide. It is worth including low-GI foods, such as whole grains, vegetables and pulses, in your daily diet – it's the variety that matters.

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