Carbohydrates vary greatly with regard to how rapidly they increase blood sugar levels. Some types of carbohydrate food are quickly absorbed and tend to make blood glucose levels increase very rapidly (‘high GI’ foods) while others which release glucose more slowly, have little effect (‘low GI’ foods). To make this easy to understand carbohydrates have been ranked on a scale of 1 to 100. Glucose has a ranking of 100 on this scale and is used as a reference against which the other foods are placed.
The Glycaemic index is only one factor to be considered when planning a healthy, balanced diet.
There are many sources of information which provide the GI rating of carbohydrates. Often, for ease of understanding, list are arranged into three categories ‘low’ ‘medium’ and ‘high’ GI foods.
Not necessarily. Some low GI foods are high in fat which cause them to be absorbed more slowly. For example milk chocolate has a low GI value. Certain ‘healthy’ foods have a high GI value e.g. ‘WeetabixR’.
These help you avoid large swings in blood sugar and also help reduce feelings of hunger.
You absorb low GI carbohydrates more slowly, therefore your blood glucose does not increase as quickly. This slow absorption also helps prevent hypos.
Understanding the glycaemic index of the foods you eat will not in itself, help you lose weight. Low GI foods do reduce hunger between meals and may help you avoid snacking between meals. Over time this can help you lose weight.
Unfortunately having meals of mixed content makes it difficult to interpret the Glycaemic index. GI charts refer to the GI value of carbohydrates when eaten on their own. When you eat a mixture of foods as a meal, the GI content of the meal is influenced by the non-carbohydrate foods which affects rate of absorption. This makes it difficult to interpret. The GI index may also be altered by cooking. If low GI foods are included at each meal, this lowers the overall glycaemic effect of the meal.
GI diets require a good understanding of the GI concept. It is possible to eat a high fat high salt diet which has a low GI index yet is certainly unhealthy.
(Courtesy of Ruth Whymark, Dept of dietetics, West Suffolk Hospital)
Oats, no added sugar muesli, bran cereals, Ready Brek, porridge or Cheerios.
Whole grain/granary/high fibre white bread toast.
Whole grain/granary/high fibre white bread sandwich, soup containing pulses (peas, beans, lentils), jacket potato with baked beans, beans on toast, filled pitta bread, fruit and/or diet yoghurt.
Based around GI low starchy food such as new potatoes, rice, pasta, noodles, sweet potato.
Add sweetcorn and/or pasta to stews and casseroles.
Include a generous portion of vegetables.
Diet yoghurt with fruit, no-added-sugar custard, milky desserts with artificial sweetener, occasional vanilla ice cream, sugar free jelly.
Fresh fruit or fruit in natural juice, diet yoghurt, oat cakes/oat based cereal bar, whole grain crackers, malt loaf and tea bread, small packet of crisps, small packet of unsalted nuts, plain popcorn, digestive biscuit.
Yes, there are times when it is necessary to eat foods with a high glycaemic index. After exercise high GI foods help replenish muscle glycogen stores.
Dr Nishan Wijenaike
West Suffolk Diabetes Service
Bury St Edmunds, Suffolk