The glycemic index was developed by David JA Jenkins who introduced it in 1981 as a tool to help manage type 1 diabetes. To better define the glycemic index of a food the following simple formula describes how a number is generated:
Glycemic Index (test food) =
Blood sugar change (Averaged) over two hours (of a test food) divided by the
Blood sugar change (Averaged) over two hours (of a reference food)
Therefore a test food, say an apple, is consumed with the resulting blood glucose measured frequently over two hours following consumption. In the same test subjects (to be able to compare the apple to something) a reference food is later consumed and blood glucose is again measured over a two hour period following consumption. The food used for the reference is usually 50 grams of pure glucose or 50 grams of available carbohydrate from white bread. Typically the number reported for the glycemic index of a food is a fraction. The blood sugar change over two hours with a reference food such as 50 grams of pure dextrose results in a higher blood sugar level than most all foods, including the apple. The larger the reported number, the higher the blood sugar from a test food compared to the reference. A glycemic index of 1.0 means the food in quesiton releases the same amount of glucose as a test meal of 50 grams of pure glucose. For the apple, the result is the following:
Glycemic Index (Apple) = 0.66
Rather than report a percentage or fraction, the number is usually just reported as 66.
So what does the number mean? In essence, it means if you compare equal amounts of carbohydrate from an apple and a reference food, the carbohydrate from the apple converted to glucose in the gut, leads to 66% of the blood glucose one would experience by eating the same amount of carbohydrate found in pure glucose.
Seems pretty straightforward. A food high in fiber would release very little digestable carbohydrate thus resulting in a lower glycemic index compared to a readily digestable carbohydrate like a potato. Some typical glycemic index values are as follows:
Reference: Kaye Foster-Powell, et al. International table of glycemic index and glycemic load values: 2002 American Journal of Clinical Nutrition 2002;76:5-56
Rice (white) studied in Canada = 72
Kelloggs All Bran Cereal studied at Battle Creek, MI = 38
Bagel (white) studied in Canada = 72
Coca Cola studied in Australia = 53
Coca Cola studied in Atlanta = 63
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A Point of View
Modern Western society is awash in a sea of food affluence. For many of us, from the moment we arise in the morning to the time we fall asleep at night, the one rhythmic pattern occurring daily with anticipated consistency is food intake—and in many cases very high quality food intake. Even the smallest of excess calories consumed daily translates over time to excess energy being stored as fat in adipose tissue.
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Overeating has become the symptom of a cultural disease associated with conditioned food intake, not a mystical physiologic process involving genes gone wild. From one diet manual to the next, the book offerings to navigate this mess are fancied up versions of the same old thing, eventually returning the dieter to a conditioned system of eating behavior. The contention of this blog, is it's time to get off the merry-go-round of dieting and learn the ABC's of basic nutritional science. Teach your children what they need to know to navigate the gauntlet of foods in the 21st century. We encourage any experts in the field to contribute.
6 comments:
Why the big difference between Australia and Atlanta?
Probably the sweetener in Australia is not HFCS but sugar, which has a higher GI according to the post from yesterday.
Wayne and Sefaly: Thanks for the comments. Actually the formula for Coca Cola is uniform between countries, but the study or test subject were different. I will address this issue in the next installment of the Glycemic Index (GI), examining what I consider are severe limitations and minimal practical applications of this measure. In short, I posted those values to show that variability between study subjects and if you pull the reference I gave, you will see tremendous variability between countries, varieties of foods like apples, rice, breads, and uniform products like Coca Cola and breakfast cereals.
Is the Coke master formula really the same? In the UK, Coke bottles say they contain sugar, not HFCS.
Even if the Coke master formula is the same but the bottling happens locally which means that the quality of water determines many of the final product's quality and taste. Which is why Coke tastes slightly different from a bottling plant in say, Bangalore versus one from a bottling plant in say, Edinburgh. This is comparing cans or bottles. From the fountain, it always tastes different from the bottle or can. May be its glycemic index is also affected by the type of water?
Actually, I may be wrong. I was under the impression coke was uniform between countries, but as you suggested, it might not be. Could multiple recipies exist and might those recipies reflect regional taste preferences? Possibly. Would all that affect the glycemic index? Definitely.
The topic of coke's formula is one that has offered up much speculation. Take a trip to Wickipedia and look it up. The possible formlas have some sweetened with HFCS and some with sugar.
Thanks. I think the most we can do about Coke master formula is speculate. A 'trade secret' is the only intellectual property tool that does not require any public declarations.
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