Forget about simple sugars and complex carbs. These days, carbs are classed according to their glycaemic index, or GI. Here's how it works.
A new way of looking at carbs
For a long time, because of their molecular structure, we’ve thought of simple sugars found in sweet foods such as sweets, fizzy drinks etc as "fast" and complex carbohydrates, found in foods containing starch (bread, pasta, rice, cereals) as "slow". The former were deemed to produce a short peak in blood sugar levels, and the latter were said to fill you up and release long-lasting energy. But the glycaemic index turned all this on it's head. GI is measured by the speed at which glucose in foods is released into the body and absorbed by the bloodstream (in other words, its ability to increase blood sugar levels). Compared to GI, the simple/complex classification is too simplistic because it's not necessarily the simple sugars that are the quickest.
Examples
Foods are ranked on a scale from 0 - 100, with glucose, the most hyperglycaemic sugar, at 100. The nearer a food's value is to 100 on the scale, the faster it is at releasing glucose. The nearer it is to 0, the slower it is. As carbohydrates are the only foods that affect blood sugar levels during their metabolisation, they are the only group that have a glycaemic index.
FoodGI
Glucose
100
Instant/parboiled rice
85
Cornflakes
85
Cooked carrot
85
Mashed potato
80
Watermelon
75
Sugar
70
Soft drinks
70
Biscuits
70
White bread
70
Sorbet
65
Wholemeal bread
65
Muesli
65
Jam
65
Boiled/steamed potato
65
Pizza
60
FoodGI
Ripe banana
60
Basmati rice
50
Wholewheat pasta
50
Kiwi
50
Grapes
45
Al dente spaghetti
40
Prune
40
Natural yoghurt
35
Quinoa
35
Apple
35
Green peas
35
Tomato
30
Raw carrot
30
Red berries and currants
25
Dark chocolate
25
Avocado
10
GI = Great Idea?
Specialists and official organisations agree that carbohydrates are a major factor in weight gain. Carbs with a high glycaemic index are quickly absorbed by the body and tend to be stored as fat. By causing a peak then a sharp drop in insulin levels in the blood, they also encourage energy slumps and hunger pangs. So the glycaemic index is a useful slimming tool: if you prioritise foods with a low glycaemic index over and above those with a high index, you'll lose weight. This is the main principle of the famous Montignac method. The glycaemic index is also fundamental in the treatment of diabetes, and it’s important for balancing your diet if you do a lot of exercise.
Its limits
GI has revolutionised diets, but should still be taken with a pinch of salt.
- The glycaemic index of a food isn’t fixed. It varies according to how the food is cooked, prepared, heated or chilled. For example, mashed potatoes have a higher glycaemic index than boiled potatoes, and the same applies to cooked carrots, which have a higher GI than raw ones. It also varies according to the food that you combine on your plate or in a dish: certain combinations can change the glycaemic index of individual foods. For example, the glycaemic index of a meal is reduced if it’s eaten with fat. It also depends on each individual’s activity levels, muscular mass and how their pancreas functions.
- You shouldn’t rely on GI alone. Think about the overall characteristics of a food: certain foods have a low glycaemic index (chocolate bars, crisps, biscuits, etc) but are high in fat and calories, so obviously you shouldn’t gorge on them! Others may have a high glycaemic index but be low in carbohydrate and fat (such as carrots).
- The glycaemic index can therefore be useful provided that you know how to interpret it and that you take into account the many other factors involved in eating a balanced diet.
