What is the Glycaemic Index?
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.
The Glycaemic index (GI) is a ranking of carbohydrates on a scale from 0 to 100 according to the extent to which they raise blood sugar levels after eating. Foods with a high GI are those which are rapidly digested and absorbed and result in marked fluctuations in blood sugar levels. Low-GI foods, by virtue of their slow digestion and absorption, produce gradual rises in blood sugar and insulin levels, and have proven benefits for health. Low GI diets have been shown to improve both glucose and lipid levels in people with diabetes (type 1 and type 2). They have benefits for weight control because they help control appetite and delay hunger. Low GI diets also reduce insulin levels and insulin resistance.
Recent studies from Harvard School of Public Health indicate that the risks of diseases such as type 2 diabetes and coronary heart disease are strongly related to the GI of the overall diet. In 1999, the World Health Organisation (WHO) and Food and Agriculture Organisation (FAO) recommended that people in industrialised countries base their diets on low-GI foods in order to prevent the most common diseases of affluence, such as coronary heart disease, diabetes and obesity.
What is the Significance of Glycaemic Index?
- Low GI means a smaller rise in blood glucose levels after meals
- Low GI diets can help people lose weight
- Low GI diets can improve the body's sensitivity to insulin
- High GI foods help re-fuel carbohydrate stores after exercise
- Low GI can improve diabetes control
- Low GI foods keep you fuller for longer
- Low GI can prolong physical endurance
How does one know what the GI value is?
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.
• Low – GI index <55
• Medium – GI index 55-69
• High – GI index 70 – 100
Measuring the GI
To determine a food's GI rating, measured portions of the food containing 10 - 50 grams of carbohydrate are fed to 10 healthy people after an overnight fast. Finger-prick blood samples are taken at 15-30 minute intervals over the next two hours. These blood samples are used to construct a blood sugar response curve for the two hour period. The area under the curve (AUC) is calculated to reflect the total rise in blood glucose levels after eating the test food. The GI rating (%) is calculated by dividing the AUC for the test food by the AUC for the reference food (same amount of glucose) and multiplying by 100. The use of a standard food is essential for reducing the confounding influence of differences in the physical characteristics of the subjects. The average of the GI ratings from all ten subjects is published as the GI of that food.
The GI of foods has important implications for the food industry. Some foods on the Australian market already show their GI rating on the nutrition information panel. Terms such as complex carbohydrates and sugars, which commonly appear on food labels, are now recognised as having little nutritional or physiological significance. The WHO/FAO recommend that these terms be removed and replaced with the total carbohydrate content of the food and its GI value. However, the GI rating of a food must be tested physiologically and only a few centres around the world currently provide a legitimate testing service. The Human Nutrition Unit at the University of Sydney has been at the forefront of Glycaemic index research for over two decades and has tested hundreds of foods as an integral part of its program. Jennie Brand Miller (JBM) is the senior author of International Tables of Glycaemic Index published by the American Journal of Clinical Nutrition in 1995 and 2002.
What is the advantage of eating low GI food?
These help you avoid large swings in blood sugar and also help reduce feelings of hunger.
How do low GI foods help diabetes control?
You absorb low GI carbohydrates more slowly, therefore your blood glucose does not increase as quickly. This slow absorption also helps prevent hypos.
How does this help me control my weight?
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.
What makes it complicated?
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.
Is there any disadvantage in following a GI diet?
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.
Examples of low GI foods and how to include them in a diet:(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.
How to Switch to a Low GI Diet
- Use breakfast cereals based on oats, barley and bran
- Use "grainy" breads made with whole seeds
- Reduce the amount of potatoes you eat
- Enjoy all types of fruit and vegetables (except potatoes)
- Eat plenty of salad vegetables with vinaigrette dressing
Hermesetas Granulated with Fructofibres contains 40% prebiotic dietary fibres and has been extensively tested according to the WHO protocol for the determination of the Glycaemic Index.
A Glycaemic Index ( GI value ) of 51 has been determined for Hermesetas Granulated with Fructofibres and thus Hermesetas Granulated with Fructofibres qualifies for a low GI product.