The Glycaemic Index (GI) is a way of ranking individual foods according to the effect they have on blood-sugar levels, that is, how quickly they are digested. The rate at which foods are digested depends on the total amounts of fat, protein, carbohydrate and fibre they contain, with the carbohydrate component in particular affecting blood-sugar levels.
Foods with a low GI ranking cause a slow, steady rise in blood-sugar levels, and high GI foods cause a rapid rise. If you eat a low GI food at the same time as a high GI food, the overall effect will be a combination of the individual effects - a moderate rise in blood sugars. Rapid rises and falls in blood sugar affect energy levels and cause cravings, so can trigger overeating.
Processing, refining and cooking food makes the carbohydrate more digestible, and also raises the GI ranking. High-fibre and natural wholefoods (whole grain or whole wheat) take longer to digest and so have a lower GI. These foods raise the blood-sugar level slowly, making them the best choice for people with diabetes and those seeking to manage their weight and improve their overall health.
Achieving a balance between high and low GI foods helps us to select a healthier diet. Including more low GI foods in your diet will provide a feeling of fullness and control post-meal highs and lows in blood-sugar levels.
Carbohydrates form an essential part of a balanced diet. They supply glucose, which is the preferred energy source for the brain. They are also an important source of vitamins and minerals, vital for good health.
The carbohydrate food group includes sugars, starches and fibre. Dietary sources of carbohydrate include bread, cereals, rice, pasta, fruit, legumes, potatoes and other root vegetables - these are starchy carbohydrates. Foods containing higher levels of sugars - such as cakes, biscuits, pastries, sugary drinks, ice cream and confectionery - should be eaten only in moderation and not every day.
Understanding how different types of carbohydrate affect blood-sugar levels is particularly important for people with diabetes. This is a condition in which the amount of sugar in the blood is too high due to insufficient insulin production. For this reason, people with diabetes are advised to cut down on sugary foods. Some scientific studies have shown that meals containing low GI foods are helpful for managing diabetes by improving both blood-sugar levels and the rate of fat metabolism. Studies have also identified that diets favouring low GI foods are an important factor in preventing the onset of Type II diabetes.
Because we eat many different types of foods over the course of a day, it is the overall balance of foods that is important, not just individual GI rankings. Examples of low, medium and high GI foods are given below.
Pure glucose has a value of 100 because it produces the greatest rise in blood-sugar levels.
All other foods are ranked from 0 to 100 according to their effect on blood-sugar levels.
High GI - 70 or more:
High GI food:
White bread, baked potatoes, highly refined breakfast cereals, French fries, mashed potatoes, white rice.
Medium GI - 56 to 69
Medium GI food:
basmati rice, bananas, rolled oats, sweetcorn, pineapple.
Low GI - 55 or less
Low GI food
- Add sliced fruit to whole grain breakfast flakes
- Milkshake made from semi-skimmed milk and fresh fruit
- Fruit such as peaches and raspberries, sliced and mixed with low fat natural yogurt
- Porridge with raisins
- Mixed grain bread with avocado or Marmite
- Flatbread with houmous and tomatoes
- Fresh fruit salad with natural low fat yogurt
- Green salad with cooked pulses and whole grain bread
- Jacket potato with baked beans and a sprinkle of cheese
- Spaghetti Bolognese served with a green salad
- Stir-fried chicken breast with mixed green vegetables and noodles
- Grilled steak with new potatoes, sweetcorn and peas
- Spicy dahl with rice and chutney
Nutrition Advice Service
Tel: 0800 188884
Other useful contacts
Find GI values of common foods at Australia's University of Sydney Human Nutrition Unit website www.glycemicindex.com (this link opens a new window).