BASICS ON GI AND GL
People are so nutrition savvy these days throwing around many nutrition terms but often these terms are misunderstood. Think of the acronym GI – Glycaemic Index – many of us know these are healthier options but why is this the case? Let’s take a closer look at Glycaemic Index (GI) and Glycaemic Load (GL).
WHATS THE FUSS AROUND GLYCAEMIC INDEX?
According to the GI Foundation of South Africa (GIFSA), 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. Foods are ranked on a scale from 0 – 100, according to their actual effect on blood glucose levels.1
55 or less
56 - 69
70 or more
Eaten with exercise
- Making sense of the GI ranges?
Low GI foods mean that your body releases and absorbs glucose (sugar) more slowly and steadily, this leads to a more suitable post-prandial (after meal) blood glucose level. Low GI foods also keep us fuller for longer. Whereas high GI foods are the opposite, these release and absorb glucose quickly and result in high blood glucose levels. Therefore, high GI options should be eaten less.
- Factors influencing the GI of food
- 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
- Al dente pasta has a lower GI than soft-cooked pasta.
- Food eaten alone vs. combined with other foods
- when high GI foods are eaten in combination with low GI foods, it results in balanced blood glucose levels.2
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.
- GI and meal planning
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 vegetables, fruit, legumes, low GI starches and/or dairy. Also remember that some high GI foods may be nutrient dense we just need to watch our portion sizes, for example some fruits and vegetables, 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.
WHATS THE FUSS AROUND GLYCAEMIC LOAD?
The glycaemic load (GL) is referred to as the “power” the food has in affecting your blood glucose levels. It was developed to address the concern that the GI concept classifies carbohydrate foods as either “good” or “bad”. However we do not like to classify foods into black and white categories, there is always a grey area – carbohydrates can definitely be incorporated into a healthy balanced meal we need to look at the type, amount, what it’s been eaten with and the timing of carbohydrates. For example, eating a high GI food after exercise is recommended as it is broken down and absorbed into the blood quickly in order to replenish muscle and liver glycogen stores.
- Calculating Glycaemic Load
The GL is calculated by taking the percentage carbohydrate content per portion of a specific food and multiplying it by its Glycaemic Index value.
GL = Carbohydrate content per portion x GI
The GL concept considers both the quantity as well as the quality of the carbohydrates eaten. The GL cut offs3 are as follows:
11 - 19
- What about when low GI foods are eaten in large quantities?
There is a saying everything in moderation and that is true for GI as well. For example, apples have a GI of 38 (Low GI) and the GL of one medium apple is 5 (Low GL). 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 apples, its GL would be 50, which will have a huge effect on your blood glucose levels and therefore is not recommended. The GI foundation of SA (GIFSA) recommends keeping your total GL per day under 100 and trying not to have high GI and GL at the same time as this will cause your glucose levels to increase substantially.
Therefore the take home message here is not to be too hung-up on eating only low GI or only low GL 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. As we said before, most carbohydrate foods can be incorporated into a healthy balanced diet and is dependent on when, what you eat it with and how much is eaten at a time.
For more information on GI or GL and which foods are classified into certain categories refer to http://www.gifoundation.com/ or chat to your dietician.
- 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