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Glycemic Index

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* Even when the Glycemic Responses are normalized to that of glucose, there are still remarkably high levels of variability. The diagram below shows that white bread, which is typically reported as having a Glycemic Index of around 71 has some individuals with extremely low Glycemic Index responses, and some that are much higher. Even fructose has some individuals with an indicated Glycemic Index of over 100, when the literature indicates it is generally around 19.<br/>[[File:ZeeviF3 I K.jpg|none|thumb|400px| The variability when three standardized meals are normalized to the individuals Glycemic Response for glucose.]]
* This individual variability is a nicely shown in the blood glucose responses shown below. These graphs show the responses of two individuals to glucose and bread. Each test was repeated, giving two lines for each participant's response to each of the two foods. You can see that each participant had reasonably similar responses each time they ate each of the foods. However, the top participant had a much higher Glycemic Response to glucose than a bread, this is what would be expected from the published Glycemic Index values. However, the participant in the lower graph has an inverted response, with higher glycemic response to bread than glucose.<br/>[[File:ZeeviF2 E.jpg|none|thumb|300px| The blood glucose responses to the standardized meals of glucose and bread for two individuals.]]
* The cloths graphs below show two individuals Glycemic Response to an honors bananas and cookies. Here you can see the individuals had opposite responses to the two foods. Personally, I am a little cautious in interpreting this data as the honors bananas and cookies were not standardized. It's possible that the top participant had an extremely ripe banana, and a high fat cookie, while the lower participant had an unripe banana, and a low fat cookie.<br/>[[File:ZeeviF2 G.jpg |none|thumb|300px| The blood glucose response to anonymous and cookies in two individuals.]]
* While the study found large variability, it also found that the average Glycemic Response generally corresponded well to the published figures.<br/>[[File:ZeeviF2 F.jpg|none|thumb|300px| The average Glycemic Response in absolute terms to various foods.]]
The research team used the data from the 800 participants to create a computer model to predict the Glycemic Response of a further hundred subjects. This computer model was able to predict the Glycemic Response surprisingly well (r=0.70 for those into statistics.) Analysis of the computer model revealed a number of factors that tend to predict the glycemic response.
* The study analyzed the digestive bacteria from stool samples, and found 21 beneficial strains and 28 non-beneficial strains of bacteria.
All this suggests that while the published Glycemic Index values are a useful rough guide to the health implications of various foods, they don't show the whole picture. It is possible to measure your own glycemic response, and I have some recommended [[Blood Glucose| Blood Glucose Meters]]. While it is impractical to perform this type of test on a wide variety of foods, I've measured my own glycemic response to a few of the meals that I eat most commonly. This measurement must be performed first thing in the morning on an empty stomach. Simply measure your fasting blood glucose, consumer the meal, then check your blood glucose over the next two hours. Measuring at 15, 30, 45, 60, 90, and 120 minutes will give you a standardized curve, but you could probably get away with far fewer measurements to get an approximation. You could normalize your values to a standardized meal, but I simply used an absolute value so that I could confirm what I was eating was not creating a health problem for me.
=How Exercise Changes Glycemic Index=
I found no studies that looked at how exercise changes the Glycemic Index of foods. The evidence available from looking at diabetic subjects suggests that exercise will lower the Glycemic Index of food consumed post exercise, and the effects of the exercise might last for up to 24 hours.
* A study showed that 30 minutes of cycling was 15 minutes after eating white bread reduced the Glycemic Index by about a third<ref name="RasmussenLauszus1994"/>. However, this study was on type-1 Diabetics and the subjects had a constant infusion of insulin.
* Another study found that 45-60 minutes of exercise reduced their blood glucose level for the following 24 hours<ref name="Van Dijk-2013"/>.
* Studies of type-2 diabetics suggest that exercise generally lowers blood glucose (as measured by [ HA1c])<ref name="Boulé-2001"/><ref name="SnowlingHopkins2006"/>.
=Simple and Complex Carbohydrates=
At one time, it was believed that "simple carbohydrates" had high Glycemic Index, while "complex carbohydrates" had lower Glycemic Indexes<ref name="ND"/>. The difference between simple and complex carbohydrates is based on the chemistry of the carbohydrate molecule, with small molecules like sugar considered "simple" and big molecules like bread considered "complex". This division into simple and complex is unfortunately crap (biochemistry term meaning 'not useful'). The digestion of carbs is a sophisticated system that does not follow this simple division. Some simple carbs (Fructose) are very slow to digest, whereas some complex carbs (maltodextrin) are very easy to digest. For instance, white bread (a "complex" carb, GI 70) has a higher Glycemic Index than table sugar (a 'simple' carb, GI 60). This is because highly refined flour in bread is more easily digested than table sugar (which is half fructose).
<ref name="SnowlingHopkins2006">N. J. Snowling, W. G. Hopkins, Effects of Different Modes of Exercise Training on Glucose Control and Risk Factors for Complications in Type 2 Diabetic Patients: A meta-analysis, Diabetes Care, volume 29, issue 11, 2006, pages 2518–2527, ISSN [ 0149-5992], doi [ 10.2337/dc06-1317]</ref>
<ref name="Van Dijk-2013">JW. Van Dijk, RJ. Manders, EE. Canfora, WV. Mechelen, F. Hartgens, CD. Stehouwer, LJ. Van Loon, Exercise and 24-h glycemic control: equal effects for all type 2 diabetes patients?, Med Sci Sports Exerc, volume 45, issue 4, pages 628-35, Apr 2013, doi [ 10.1249/MSS.0b013e31827ad8b4], PMID [ 23507836]</ref>
<ref name="Boulé-2001">NG. Boulé, E. Haddad, GP. Kenny, GA. Wells, RJ. Sigal, Effects of exercise on glycemic control and body mass in type 2 diabetes mellitus: a meta-analysis of controlled clinical trials., JAMA, volume 286, issue 10, pages 1218-27, Sep 2001, PMID [ 11559268]</ref>
<ref name="RasmussenLauszus1994">O. W. Rasmussen, F. F. Lauszus, K. Hermansen, Effects of Postprandial Exercise on Glycemic Response in IDDM Subjects: Studies at constant insulinemia, Diabetes Care, volume 17, issue 10, 1994, pages 1203–1205, ISSN [ 0149-5992], doi [ 10.2337/diacare.17.10.1203]</ref>
<ref name="ZeeviKorem2015">David Zeevi, Tal Korem, Niv Zmora, David Israeli, Daphna Rothschild, Adina Weinberger, Orly Ben-Yacov, Dar Lador, Tali Avnit-Sagi, Maya Lotan-Pompan, Jotham Suez, Jemal Ali Mahdi, Elad Matot, Gal Malka, Noa Kosower, Michal Rein, Gili Zilberman-Schapira, Lenka Dohnalová, Meirav Pevsner-Fischer, Rony Bikovsky, Zamir Halpern, Eran Elinav, Eran Segal, Personalized Nutrition by Prediction of Glycemic Responses, Cell, volume 163, issue 5, 2015, pages 1079–1094, ISSN [ 00928674], doi [ 10.1016/j.cell.2015.11.001]</ref>
<ref name="Brand-MillerStockmann2008">J. C Brand-Miller, K. Stockmann, F. Atkinson, P. Petocz, G. Denyer, Glycemic index, postprandial glycemia, and the shape of the curve in healthy subjects: analysis of a database of more than 1000 foods, American Journal of Clinical Nutrition, volume 89, issue 1, 2008, pages 97–105, ISSN [ 0002-9165], doi [ 10.3945/ajcn.2008.26354]</ref>

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