What is the Glycemic Index?
Using a scale of 1 to 100, Glycemic Index- GI is a numerical index of how your blood sugar is affected within two to three hours of eating foods that are high in carbohydrates and how they turn into blood glucose. The glycemic index is about the quality of the carbohydrates, not the quantity.
Eating foods that help stabilize your blood sugar and insulin levels is the key to your long term health, and lower GI foods do just that.
Foods that are digested and absorbed faster will have a higher glycemic index of 70 and above. 55 and under is low GI, 56 to 69 is medium GI on a scale of 1 to 100.
Glucose is the reference food with a GI value of 100 and this will be the maximum value any food can have.
History of Glycemic Index
David Jenkins, a professor of nutrition at the University of Toronto invented the Glycemic Index in 1981. It was originally created to help people withdiabetes, then it led to the one of the most popular non-fad diets of today, Glycemic Index Diet.
After giving his subjects most common carbohydrate rich foods, he recorded their blood sugar levels after a specific period of time. His findings were surprising. For example, in equal quantities, white bread caused a higher spike in blood glucose levels of the subjects than ice cream!
Other nutrition and diet experts went on to test hundreds of foods in labs over the years, and these were compiled into today’s Glycemic Index Chart.
Nowadays, GI is an important part of medical nutrition in Australia and Canada. People in some areas of Europe and the United States are also slowly becoming aware of GI’s roles in weight loss, athletic performance, treatment of diabetes, heart disease and PCOS.
How is Glycemic Index Measured?
The average GI value is calculated from data collected from 10 or more volunteers. Both the standard and test food must contain an equal amount of available carbohydrate- 50 grams. The smaller the percentage of carbs in the food, the larger the portion needs to be in order to provide the standard 50 gram amount of digestible carbs.
A sample of blood is then taken from each subject every 15 minutes during the first hour and thereafter every 30 minutes. These blood samples are laboratory-tested for glucose content and the results recorded.
The GI of a food is defined as (the area under the two hour blood glucose response curve- AUC) following the ingestion of this fixed portion of carbohydrate. The AUC of the test food is divided by the AUC of the standard- either glucose or white bread, giving two different definitions- and multiplied by 100. The result gives a relative ranking for each tested food.
How to Switch to a Low GI Diet?
• Eat small, regular meals of a variety of foods from different nutrient groups: When a high-GI food is eaten with a low-GI or high-protein food, the effect of the high-GI food on blood sugar levels is reduced.
• Eat lean meats- protein and oily fish or seafood- Omega 3 fatty acids regularly every week. Cut away any visible fat on meats and choose barbecuing or grilling as cooking methods over frying. Do not use creamy high saturated fat sauces on your meat.
• Drink more water, skimmed milk- calcium and fruit juices- vitamins and minerals rather than sweet drinks that are loaded with sugar.
• Eat more nuts and seeds, more legumes, more wholegrain breads and cereals that are also low in sugar.
• You can’t go wrong with fruits and vegetables, have at least five servings every day.
*Before we continue with the info on use of glycemic index for performance, I’d like to tell you about a healthy diet program that is a favorite of mine and uses a lot of the foods with low to medium glycemic index values: Isabel de los Rios’ ‘The Diet Solution Program’.
GI for Performance
Use of Glycemic Index in exercise nutrition may have some value when considering pre- and post- training meals. These are eaten according to whether they are rated as low, medium or high.
Carbohydrates in the form of sugars are the body’s prime energy source. They are a ready source of energy that can fuel about 90 mins of continuous exercise, which represents an energy reserve of about 2000kcal within the body. Carbs are required by the body because it is the most effective means of producing energy. The GI therefore is a useful guide.
It is suggested low to moderate ranked foods- pasta, porridge be consumed several hours prior to exercise due to their long slow release of glucose into the blood stream. While high glycemic index foods- corn flakes, honey, sports drinks, sweets should be consumed during or post exercise because they quickly release glucose into the blood stream which will be rapidly taken up into the muscles.
*I’m sure you’ve noticed that there are so many different workout plans and supplements out there that claim that they can quickly help you perform better and build lean muscle quickly. You may have already tried many of them only to see money fly out of your pockets, little to no muscle gains and lots of wasted time and energy.