Health / Glycaemic Index

What is the Glycaemic Index?

Information compiled by Gabi Steenkamp, Registered Dietitian

If we consider the word glyc- aemic - index, we see that the first part refers to glucose, the second part to blood, and the third to an indicator of sorts. Thus the Glycaemic index is a “blood glucose indicator” and refers to the relative degree to which the concentration of blood glucose rises after consumption of a food. It does not indicate the actual level of glucose in the blood. Instead it shows the relative percentage of the effect of the food on blood glucose levels compared with the effect of pure glucose.

In other words, the Glycaemic index (GI) is an indicator of the rate of digestion and absorption of a carbohydrate food.

When carbohydrate foods such as starches, fruit, vegetables, dairy, legumes and sweet things are eaten; they are digested in the gut and then absorbed into the bloodstream in the form of glucose (the simplest form of sugar).

Researchers have discovered that not all carbohydrates are digested and absorbed at the same rate.  This means that different carbohydrates have different effects on blood glucose levels. This difference is called the Glycaemic Index or GI.

The Glycaemic Index (GI) can be used as a measure (or tool), on a scale from 1 to 100, of how slow or fast a carbohydrate containing food is digested and absorbed.
It thus gives an indication of the rate at which the food affects blood glucose levels after ingestion of the carbohydrate containing food.

Glucose is assigned a numerical value of 100, and is absorbed almost immediately giving a sharp, quick rise in blood glucose levels. All other carbohydrate foods are compared to this as the standard.

In some research studies, white bread has been used as the standard. If bread is used, the Glycaemic index of glucose must be higher than bread and thus all the values will be higher. For example the GI of cornflakes is 84 when tested against glucose, whereas it is 100 when tested against white bread.

In South Africa, glucose is the preferred standard, since it is more practical and easier to work against a reference food of 100. However, when consulting different Glycaemic index tables, it is important to check whether the values have been determined using bread or glucose as the reference food. And to make matters worse, many tables mix up the two without realizing it! So be very careful when you look up GI values in tables. Always check what food has been used as the reference food - glucose or bread. To convert a GI with bread as the reference food, simply multiply the value by 0,7. To convert from glucose as the reference food, to bread, multiply by 1,43.

If you are unsure, visit the website www.gabisteenkamp.co.za or use the South African Glycaemic Index and Load Guide (GIFSA 2012), to get reliable information on the Glycaemic index of different foods commonly eaten in South Africa.

Carbohydrate foods with GI values nearer 100 (high GI foods) are digested and absorbed faster than those carbohydrate foods with GI values 55 and below (low GI foods). Regular South African bread (including white and brown bread), for example, has a high GI of 72 – 81, and butter beans have a low GI of 31. This means that the bread would give a sharper and quicker rise in blood glucose than the butter beans.

From the graph above it becomes obvious that the carbohydrate supplied by the high GI bread would only give fuel to the body cells for about one hour, whereas the low GI butter beans would give a smaller, but steady trickle of fuel for 2½ - 3 hours. Thus a meal containing butter beans, or any other legume such as baked beans, would keep blood glucose levels steady for much longer than a meal based on bread. For this reason, it is important to include legumes i.e. cooked dry beans, baked beans and lentils, to as many meals as possible, so that the Glycaemic index of the whole meal may be lowered. See the recipe books Eating for Sustained Energy 1, 2, 3, 4, Sustained Energy for Kids, Snacks and Treats for Sustained Energy, Fast Food for Sustained Energy (Tafelberg) for lots of ideas on lowering the GI of meals without compromising taste.

List of low fat and low GI South African foods

Dairy

  • Milk: low fat, fat free, plain & flavoured.
  • Yoghurt: low fat, fat free, plain & sweetened
  • Custard: low fat, fat free  unsweetened  & sweetened
  • Ice cream: low fat sweetened & unsweetened

Cereals

  • Pronutro: Wholewheat  (Original and Apple Bake)
  • High Fibre Bran
  • Cold Mealiemeal
  • Oat bran

Bread

  • Provita
  • Seed loaf bread Pumpernickel
  • Low GI breads
  • Any other bread made with lots of oats, whole kernels, crushed wheat or oat bran

Starches

  • Legumes: dried beans, peas, lentils, pea dhal, baked beans,   canned beans in sauces 
  • Soya flour
  • Pasta (durum wheat)
  • Boiled barley
  • Boiled wheat (stampkoring)
  • Sweet potato
  • Mealies/corn
  • Basmati rice

Fruit

  • Deciduous fruits: apricots, cherries, peaches, plums, pears, apples, kiwi, grapes, etc.
  • Citrus fruit: oranges, naartjies, grapefruit, lemons.

Vegetables

  • All vegetables excluding pumpkins, squashes, parsnips.

Snacks Sugars

Fructose- not more than 20g per day.

  • Sugar free sweets
  • Sugar free jam
  • Homemade air popped popcorn

Drinks

  • Water – still or sparkling
  • Sugar free cold drinks
  • Juice of low GI fruits – 1 glass only!
  • Sustagen

Disclaimer: The information contained in this website is provided by the SPAR Group Ltd for general information purposes only. Any reliance you place on such information is therefore strictly at your own risk.

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