As a nutrition tool, the glycaemic index (GI) has a number of shortcomings. Some of these are, however, overcome by the so-called glycaemic load (GL).
Here are some of the latest findings on the GL, as discussed by Gabi Steenkamp during a Master Class at the 22nd Biennial Nutrition Congress in Pretoria (October 2008).
What is the GL?
The GL is the amount of carbohydrate in a portion of food that's eaten, and the rate at which this portion of food causes an increase in blood-glucose levels. The GL, therefore, gives us an indication of how much insulin the body will have to produce to deal with the increase in the blood-sugar level.
It's evident that the concept of the GL is rather more complex than that of the GI.
To calculate the GL of a portion of food, we use the following formula:
GL = grams of carbohydrate in the food portion X the GI of the food/100
A small pear contains 15g of carbohydrates and has a GI of 36, so the calculation for the GL of the pear is:
15 x 36 /100 = 5.4 = GL
What is the ideal GL?
Since the GL concept is still relatively new, researchers are still debating which GL values are ideal.
They've suggested that main meals should have a GL varying between 20 and 30, while snacks should have a GL of 10 to 15.
On a daily basis, the leaders in the field of GL research recommend that an individual’s food intake shouldn't exceed a total GL of 100-120.
A good rule of thumb is to remember that GL values below 10 generally keep blood-glucose levels low and steady.
GL values of popular foods
Steenkamp pointed out how the GL values of popular foods can vary depending on their carbohydrate content.
The GL of fruits is generally low, with deciduous fruits having lower GL values than tropical fruits (e.g. apple: 5, peach: 4, orange: 6)
However, the GL of a 300ml glass of orange juice is quite high, namely 17 (this is because the glass of orange juice contains 39g of carbohydrates).
Fruits the size of tennis balls generally have GL values varying between 5 and 10 and can, therefore, be used as healthy snacks.
Vegetables such as broccoli, cabbage and cauliflower have a low carbohydrate content and a whole plate of broccoli would only have a GL of 4.
Vegetables with a higher carbohydrate content, such as carrots, have a higher GL if you eat large portions thereof, but 2 cooked carrots also have a GL of 4, like broccoli. So, you would have to eat a smaller portion (2 carrots compared to a whole plate of broccoli) to get the same GL result.
The "free vegetables" such as tomatoes, cucumber, sweet peppers, lettuce, spinach, watercress etc, which contain very little carbohydrate, have extremely low GL values (less than 1) and can generally be eaten in large quantities.
The GL of different cereal products can vary a lot depending on the GI and the carbohydrate content of the given food, which in turn is also influenced by the size of the portion:
- 1 Provita has a GL of only 2, whereas 1 rice cake has a GL of 6.
- ½ a cup of High-fibre bran has a GL of 9, but ½ cup Special K has a GL of 18 (exactly double!).
- ½ a cup of boiled rice has a GL of 10.
- ½ a cup of baked beans has a GL of 12 (so although baked beans have a low GI, their. glycaemic load is higher than that of a cooked starch like rice).
The size of helpings also influences the GL considerably, for example a large Chelsea bun has a GL of 36, but the GL of a small Chelsea bun is much lower at 9.
Use of the GI and GL
Jeske Wellmann, who assisted with the Master Class, said that the concepts of the GI and GL are used more widely in the UK, Australia and South Africa than in the rest of the world, including the USA.
In Australia, for example, foods with a low GI are marked with the GI symbol, which is backed by the University of Sydney, the Australian Diabetes Association and the Juvenile Diabetes Research Fund. It's therefore not surprising that a recent study showed that 82% of Australians are aware of the GI and its symbol.
In South Africa, the Glycemic Index Foundation (GIFSA) also has a logo that so far is displayed on 36 foods that have a low GI, plus lower fat, saturated fat and sodium contents, and a high fibre content. Look out for the GIFSA logo when you're shopping.
Slow absorption is desirable
One characteristic of low-GI foods is that they're absorbed more slowly than high-GI foods. This means that low-GI foods make you feel full for longer and promote weight loss.
Low-GI recipe books
Steenkamp gave all the delegates at the Master Class a sample of a low-GI chocolate brownie. It was delicious and none of us could believe that this brownie, which had a GL of only 8 compared to a GL of 29 for regular brownies, had been baked with cooked white beans to lower the GI, skim milk to lower the fat content, and 50% less sugar to lower the GL.
You too can make delicious low-GI/GL dishes by applying the principles outlined in the cookbooks published by Steenkamp and co-authors. Contact her via her website at www.gabisteenkamp.co.za if you would like to obtain copies of recipe books such as Eating for Sustained Energy (three different editions are available) and Sustained Energy for Kids.
- (Dr I.V. van Heerden, DietDoc, October 2008)
(Steenkamp, G (2008) Master Class on the Glycaemic Index. 22nd Biennial Nutrition Congress on Evidence Based Nutrition Leading the Way in Innovation, University of Pretoria; www.gabisteenkamp.co.za – Accessed on 11 Oct 2008)