You hear a lot about the Glycemic Index these days, but how helpful is it for diabetics really. Some people swear by it, and some (like me) not so much.
First let’s explain what it is:
It was developed by Dr. David J. Jenkins and colleagues in 1980–1981 at the University of Toronto in their research to find out which foods were best for people with diabetes.
A lower glycemic index suggests slower rates of digestion and absorption of the foods’ carbohydrates and may also indicate greater extraction from the liver and other areas that process carbohydrate digestion. A lower glycemic response usually equates to a lower insulin demand but not always, and may improve long-term blood glucose control and cholesterol. The insulin index is also useful for providing a direct measure of the insulin response to a food, some people think even better than the glycemic index.
The glycemic index of a food is defined as the incremental area under the two-hour blood glucose response curve (AUC) (area under the curve) following a 12-hour fast and eating a food with a certain quantity of available carbohydrate (usually 50 g). 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 average GI value is calculated from data collected in 10 human subjects. Both the standard and test food must contain an equal amount of available carbohydrate. The result gives a relative ranking for each tested food
So first we see that this was a very limited sample group, 10 people. They were also not diabetic but healthy subjects. Tests were not done at normal “peak” (or highest glucose numbers reached) but at the 2 hour post-prandial levels. The foods contained in the index are also not defined by culture, so many foods are not represented.
Here’s an example of the index:
Low GI=55 or less, Med GI= 56-69, High GI=70 or more.
The idea is that low-GI foods will release glucose more slowly and steadily, which leads to lower post-prandial (after meal) blood glucose readings. The problem with this is that most people don’t eat just one food at a time, they eat a mixture of carbs, protein, and fat in a meal. Protein and fat slows the absorption rate of the carbs eaten depending on the amounts. Most people aren’t test subjects.
Another problem is that all people are more sensitive to carbs at different times of the day. Both diabetics and non-diabetics are usually more sensitive to carbs in the morning when cortisol and other hormones are highest and usually less sensitive as the day goes on. So a food eaten at breakfast might cause a much larger spike in glucose numbers than the same food eaten at dinner.
Then there’s the fact that every person is different and their response is different. I, for example, can eat a good amount of potato where other diabetics I know can’t even eat a few spoonfuls without spiking to high numbers. Everyone is different, even at different times of the day.
The glycemic value of a food can be altered by the type of food, its ripeness, processing, the length of storage, cooking methods, and the variety of the food. A very ripe piece of fruit for instance has a higher glucose level than one less ripe, the length of time pasta is cooked determines the glycemic value it has as well. Did you know that cold potato has a different effect on BG levels than hot potato? It’s true because of the way the starch is processed by your body.
The amount of a food eaten has more impact than the GI value usually. Many people eat half a piece of fruit to stay within their glucose level range. Very few people eat 50 grams of a vegetable at one time.
Many have tried to get around the problems with the GI by using the concept of glycemic load.
Here’s some more about that from my friend Andy Weil:
My position on the issue is that the GI Index is perhaps a good starting point, but I wouldn’t rely on it for food choice alone. As a matter of fact I’m a believer in the KISS method: Keep It Simple Stupid. I say develop your own personal GI Index that works for your body by using the Testing 101 method. That way you can have the most accurate information geared just for you and not 10 “healthy” subjects in a study. It’s also one less chart to look up and less math.
That’s my choice.
© EMO 5/12
Knowledge is Power