Glycaemic Index

How carbs can impact your blood glucose

The rate at which carbohydrate impacts on blood glucose depends mainly on the amount (carbohydrate load) and to a lesser extent, the type of carbohydrate (glycaemic index).

The Glycaemic Index (GI) is a scale from 1 to 100 that is used to measure how quickly foods that contain carbohydrate raise blood glucose levels. Foods that contain carbohydrate are given a GI value; foods that have little or no carbohydrates such as cheese, meat, fish and eggs will have no GI value.

Graph showing affect of different GI foods on blood glucose level

The diagram above demonstrates how low, medium and high GI foods can affect blood glucose over time.

Carbohydrate foods that break down quickly during digestion raise blood glucose more quickly, and have a higher GI value (greater than 70). Foods that break down more slowly during digestion raise blood glucose more slowly and have a lower GI value (less than 55)

The diagram above demonstrates how low, medium and high GI foods can affect blood glucose over time.


Low, Medium and High GI Foods

The table below illustrates the GI value of commonly eaten foods and drinks


Low GI

Less than 55

Medium GI

55 - 70

Higher GI

Greater than 70

Breakfast cereals

All bran cereal

All Bran, Sultana Bran, muesli, porridge oats


Instant porridge, Weetabix, Shredded Wheat, Special K


Coco Pops, Rice Krispies, Cornflakes, Cheerios


Bread, biscuits, cakes, confectionery

pumpernickel bread

Rye bread, pumpernickel bread

granary bread

Granary/multi-grain bread, pitta bread, wholemeal bread, crumpet, digestives, rich tea, crisps, chocolate

white bagel

French stick, white bread, bagel

Potatoes, rice, pasta

sweet potato

Sweet potatoes, noodles, macaroni, spaghetti

cous cous

New potatoes, boiled potatoes, cous cous, brown rice, basmati


Instant potatoes, baked potatoes, instant rice, french fries, chips

Fruit and vegetables


Apples, grapefruit, grapes, kiwis, oranges, pears, peaches, carrots, green peas


Apricots, mangoes, pineapples, raisins, sultanas, melons


Watermelon, turnip, parsnips

Beans and pulses

butter beans

Baked, butter, black, kidney beans, chick peas, lentils, nuts


broad beans

Broad beans

Milk and dairy


Milk, custard, yoghurt

ice cream

Ice cream

  • Low GI foods are not always healthy for example ice cream, nuts and chocolate all have a low to medium GI but are high in fat and calories. Such items should be eaten in small quantities.
  • High GI foods can be a good source of nutrients, for example watermelon, so do not need to be removed just because they have a rapid and large effect on blood glucose levels.
  • Focus on the overall GI content of your meal to keep blood glucose levels within target range.
  • For a healthy, balanced approach to eating, include low fat and low sugar foods with lower GI options as a basis for meals and snacks
  • The key is to use the Glycaemic Index in the context of balanced eating. A healthy way to use the GI principles is to incorporate a range of lower GI carbohydrates that are also low in fat and calories into your meals.