The Glycaemic Index (GI) is a system that ranks carbohydrate containing foods based on their physiological effect on blood glucose (blood sugar) levels. The GI of a specific food is determined by comparing the Blood Glucose Response (BGR) of that food with the BGR of glucose. Glucose is used as the reference food as it is absorbed quickly from the small intestine and results in the greatest and most rapid rise in blood glucose (GI of 100). Foods are ranked on a scale from 0 – 100, according to their actual effect on blood glucose levels.
||55 or less
||56 – 69
||70 or more
||Eaten with exercise
Food with a high GI raise blood sugar levels more than a food with a medium or low GI, therefore should be eaten less often. High and varying blood sugar levels cause appetite, mood, and metabolic changes that are all unhealthy (effects include weight gain, moodiness, and insulin resistance/diabetes). There are some factors that can influence or change the GI of a food, here they are:
- The higher the fat, protein and fibre content of a food, the lower the GI of a food.
- As a fruit or vegetable ripens and storage time is increased, the higher the GI becomes.
- Processing of food increases the GI e.g.
- Fruit juice has a higher GI than the whole fruit.
- Mashed potato has a higher GI than a whole baked potato.
- Stone-ground whole-wheat bread has a lower GI than whole wheat bread.
- Cooking method and time e.g.
- Al dente pasta has a lower GI than soft-cooked pasta.
- Food eaten alone vs. combined with other foods e.g. when high GI foods are eaten in combination with low GI foods, it results in balanced blood glucose levels.
As a general rule, foods with a lower GI tend to be high in fibre, less processed and the type of carbohydrates that are recommended as part of a healthy balanced diet. Some examples include whole-grain breads and cereals (e.g. rye or whole-wheat bread, barley), dried beans and legumes, all non-starchy vegetables and some starchy vegetables such as sweet potatoes and most fruit.
When it comes to using this concept during meal planning, choosing foods that have a low or intermediate GI will ensure you get nutritious foods that do not cause spikes in your blood sugar levels. It is okay to include small quantities of high GI foods in a meal, as long as most of the meal contains lower GI carbohydrate foods such as fruit, vegetables, fruit, legumes, low GI starches and/or dairy.
The GI gives you an indication of the type of carbohydrate, but it doesn’t tell you about how much you should be eating therefore portion control is still key. There are also some foods that are classified as being high GI but are nutrient-dense. An example of this is fruit and vegetables. Some fruits and vegetables, for example, have higher GI values and therefore perceived “bad”, but when you look at the quantity of carbohydrate per portion, their effect on your blood sugar levels will be minimal. An example of this is pumpkin. It contains only a small amount of carbohydrate and therefore if eaten in normal portion sizes e.g. ½ cup cooked, it will not impact blood glucose levels even though it is classified as high GI.
What about when low GI foods are eaten in large quantities? For example, apples have a GI of 38 (Low GI). If you eat one apple it will have a minimal effect on blood glucose levels however if you eat a whole 500 g packet of dried apples this will have a huge effect on your blood glucose levels and therefore is not recommended.
THE BOTTOM LINE: the take home message here is not to be too hung-up on eating only low GI foods but to ensure that you are choosing whole grain, high fibre and unprocessed carbohydrates as well as sticking to the recommended portion sizes depending on your needs. Most carbohydrate foods can be incorporated into a healthy balanced diet with a little care.
For more information on GI and which foods are classified into certain categories refer to http://www.gifoundation.com/ or chat to your dietician.
This content is provided by FUTURELIFE®
- Alan W. Barclay, Jennie C. Brand-Miller, Thomas M.S. Wolever. Glycemic Index, Glycemic Load, and Glycemic Response Are Not the Same. Refer to link http://care.diabetesjournals.org/content/28/7/1839.long