The glycaemic index (GI) is a rating system that shows how quickly each food affects your blood sugar (glucose) level when that food is eaten on its own.
The GI index runs from 0 to 100 and usually uses pure glucose, which has a GI of around 100, as the reference. Slowly absorbed carbohydrates have a low GI rating (55 or below), and include most fruits and vegetables, unsweetened milk, nuts, pulses, some wholegrain cereals and bread.
Carbohydrate foods that are broken down quickly by your body and cause a rapid increase in blood glucose have a high GI rating. High GI foods can include white bread and rice, sugary soft drinks, and potatoes.
Low or medium GI foods are broken down more slowly and cause a gradual rise in blood sugar levels over time. Some examples are pulses, some fruit and vegetables, and wholegrain foods e.g. porridge oats.
The GI and Diabetes
The glycaemic index can be useful for people with type 2 diabetes because eating foods with low GI ratings can help control blood glucose.
However, the bigger picture must also be considered. Research has found that the biggest influence on blood glucose levels is the amount of carbohydrate eaten, not necessarily its GI rating. Diabetes UK have more specific guidance.
What else affects GI?
- Different cooking methods, e.g. frying, boiling and baking.
- How the food has been processed and the ripeness of fruit and certain vegetables
- Fibre: wholegrains and high-fibre foods act as a physical barrier that slows down the absorption of carbohydrate.
- Fat and protein lower the GI of food. Chocolate has a low GI because of its fat content, as do dairy products which are also high in protein.