Glycemic Index (GI) is a measure of how much a food raises blood glucose (blood sugar). A food with a higher Glycemic Index raises the blood sugar more than a food with a lower Glycemic Index. The Glycemic Index value is based on a comparison with a reference food, normally either white bread or glucose.
1 Calculating the Glycemic Index
The Glycemic Index is calculated by measuring blood glucose periodically after the consumption of the food. Typically the measurements are taken just before consuming the food, then at 15, 30, 45, 60, 90, and 120 minutes. These measurements provide a blood glucose curve, and the area between the curve and the baseline measurement taken just before consuming the food is the "incremental Area Under the Curve" (iUAC). The iUAC is compared with the iUAC for a reference food and the value given as a percentage. So a Glycemic Index of 50 means that the food raises the blood sugar by 50% of the reference food. Generally the portion of test food consumed contains 50 grams of carbohydrate. (The iAUC is sometimes called the Post Prandial Glycemic Response or PPGC.)
2 Glycemic Index and Health
High blood glucose levels are linked to many health problems.
- High Glycemic Index foods may be associated with obesity which constitutes a major health risk.
- Lower Glycemic Index foods are considered critical to preventing metabolic syndrome, as it is the high Glycemic Index foods that are risk factors, not carbohydrates as a whole .
- Elevated blood glucose after consuming food (Postprandial Hyperglycemia) is an independent risk factor for heart disease and high blood pressure .
- Postprandial Hyperglycemia is associated with an increased risk of stroke and heart attacks.
- Postprandial Hyperglycemia is associated with the risk of death in both diabetics and the overall population, independent of age, blood pressure, cholesterol, body mass index, and smoking habit .
- Lower Glycemic Index foods may improve HDL (Healthy) Cholesterol levels.
- Elevated blood glucose and insulin are associated with cancers of the colon, breast, and prostrate. It's been suggested that the high mortality rate from most cancers in obese subjects may be due to elevated insulin
- Diets with Lower Glycemic Index foods may help manage Impaired Glucose Tolerance (IGT)
- IGT is a risk factor for Type 2 Diabetes, with estimates that 70% of those with IGT will eventually develop Diabetes, with 5-10% succumbing each year.
- IGT is also linked with metabolic syndrome, which is the cluster of health problems including obesity, high blood pressure, non-alcoholic fatty liver disease, elevated triglycerides, and cardiovascular disease. (Note that while glucose lowering drugs may help prevent the conversion of IGT to Diabetes, but it's unclear if they will help prevent some of the health complications of diabetes.)
- IGT is a risk factor for liver cirrhosis and survival rates for those with liver cirrhosis.
3 Simple and Complex Carbohydrates
At one time, it was believed that "simple carbohydrates" had high Glycemic Index, while "complex carbohydrates" had lower Glycemic Indexes. 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).
- 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
- Susan B. Roberts, High-glycemic Index Foods, Hunger, and Obesity: Is There a Connection?, Nutrition Reviews, volume 58, issue 6, 2009, pages 163–169, ISSN 00296643, doi 10.1111/j.1753-4887.2000.tb01855.x
- JC. Brand-Miller, SH. Holt, DB. Pawlak, J. McMillan, Glycemic index and obesity., Am J Clin Nutr, volume 76, issue 1, pages 281S-5S, Jul 2002, PMID 12081852
- DS. Ludwig, JA. Majzoub, A. Al-Zahrani, GE. Dallal, I. Blanco, SB. Roberts, High glycemic index foods, overeating, and obesity., Pediatrics, volume 103, issue 3, pages E26, Mar 1999, PMID 10049982
- Ryan K. Masters, Eric N. Reither, Daniel A. Powers, Y. Claire Yang, Andrew E. Burger, Bruce G. Link, The Impact of Obesity on US Mortality Levels: The Importance of Age and Cohort Factors in Population Estimates, American Journal of Public Health, volume 103, issue 10, 2013, pages 1895–1901, ISSN 0090-0036, doi 10.2105/AJPH.2013.301379
- G. Riccardi, AA. Rivellese, Dietary treatment of the metabolic syndrome--the optimal diet., Br J Nutr, volume 83 Suppl 1, pages S143-8, Mar 2000, PMID 10889805
- JL. Chiasson, RG. Josse, R. Gomis, M. Hanefeld, A. Karasik, M. Laakso, Acarbose treatment and the risk of cardiovascular disease and hypertension in patients with impaired glucose tolerance: the STOP-NIDDM trial., JAMA, volume 290, issue 4, pages 486-94, Jul 2003, doi 10.1001/jama.290.4.486, PMID 12876091
- C. Stettler, S. Allemann, P. Jüni, CA. Cull, RR. Holman, M. Egger, S. Krähenbühl, P. Diem, Glycemic control and macrovascular disease in types 1 and 2 diabetes mellitus: Meta-analysis of randomized trials., Am Heart J, volume 152, issue 1, pages 27-38, Jul 2006, doi 10.1016/j.ahj.2005.09.015, PMID 16824829
- KT. Khaw, N. Wareham, R. Luben, S. Bingham, S. Oakes, A. Welch, N. Day, Glycated haemoglobin, diabetes, and mortality in men in Norfolk cohort of european prospective investigation of cancer and nutrition (EPIC-Norfolk)., BMJ, volume 322, issue 7277, pages 15-8, Jan 2001, PMID 11141143
- ES. Ford, S. Liu, Glycemic index and serum high-density lipoprotein cholesterol concentration among us adults., Arch Intern Med, volume 161, issue 4, pages 572-6, Feb 2001, PMID 11252117
- G. Frost, AA. Leeds, CJ. Doré, S. Madeiros, S. Brading, A. Dornhorst, Glycaemic index as a determinant of serum HDL-cholesterol concentration., Lancet, volume 353, issue 9158, pages 1045-8, Mar 1999, PMID 10199351
- G. McKeown-Eyssen, Epidemiology of colorectal cancer revisited: are serum triglycerides and/or plasma glucose associated with risk?, Cancer Epidemiol Biomarkers Prev, volume 3, issue 8, pages 687-95, Dec 1994, PMID 7881343
- E. Giovannucci, Insulin and colon cancer., Cancer Causes Control, volume 6, issue 2, pages 164-79, Mar 1995, PMID 7749056
- Paul J. Limburg, Rachael Z. Stolzenberg-Solomon, Robert A. Vierkant, Katherine Roberts, Thomas A. Sellers, Philip R. Taylor, Jarmo Virtamo, James R. Cerhan, Demetrius Albanes, Insulin, Glucose, Insulin Resistance, and Incident Colorectal Cancer in Male Smokers, Clinical Gastroenterology and Hepatology, volume 4, issue 12, 2006, pages 1514–1521, ISSN 15423565, doi 10.1016/j.cgh.2006.09.014
- L. Baglietto, DR. English, JL. Hopper, HA. Morris, WD. Tilley, GG. Giles, Circulating insulin-like growth factor-I and binding protein-3 and the risk of breast cancer., Cancer Epidemiol Biomarkers Prev, volume 16, issue 4, pages 763-8, Apr 2007, doi 10.1158/1055-9965.EPI-06-0960, PMID 17416768
- GA. Lima, LL. Corrêa, R. Gabrich, LC. Miranda, MR. Gadelha, IGF-I, insulin and prostate cancer., Arq Bras Endocrinol Metabol, volume 53, issue 8, pages 969-75, Nov 2009, PMID 20126849
- AW. Hsing, YT. Gao, S. Chua, J. Deng, FZ. Stanczyk, Insulin resistance and prostate cancer risk., J Natl Cancer Inst, volume 95, issue 1, pages 67-71, Jan 2003, PMID 12509402
- A. W. Hsing, S. Chua, Y.-T. Gao, E. Gentzschein, L. Chang, J. Deng, F. Z. Stanczyk, Prostate Cancer Risk and Serum Levels of Insulin and Leptin: a Population-Based Study, JNCI Journal of the National Cancer Institute, volume 93, issue 10, 2001, pages 783–789, ISSN 0027-8874, doi 10.1093/jnci/93.10.783
- DB. Boyd, Insulin and cancer., Integr Cancer Ther, volume 2, issue 4, pages 315-29, Dec 2003, doi 10.1177/1534735403259152, PMID 14713323
- Thomas M. S. Wolever, Christine Mehling, High-carbohydrate–low-glycaemic index dietary advice improves glucose disposition index in subjects with impaired glucose tolerance, British Journal of Nutrition, volume 87, issue 05, 2007, pages 477–487, ISSN 0007-1145, doi 10.1079/BJN2002568
- DM. Nathan, MB. Davidson, RA. DeFronzo, RJ. Heine, RR. Henry, R. Pratley, B. Zinman, Impaired fasting glucose and impaired glucose tolerance: implications for care., Diabetes Care, volume 30, issue 3, pages 753-9, Mar 2007, doi 10.2337/dc07-9920, PMID 17327355
- Nidhi Bansal, Prediabetes diagnosis and treatment: A review, World Journal of Diabetes, volume 6, issue 2, 2015, pages 296, ISSN 1948-9358, doi 10.4239/wjd.v6.i2.296
- SM. Grundy, Pre-diabetes, metabolic syndrome, and cardiovascular risk., J Am Coll Cardiol, volume 59, issue 7, pages 635-43, Feb 2012, doi 10.1016/j.jacc.2011.08.080, PMID 22322078
- T. Nishida, S. Tsuji, M. Tsujii, S. Arimitsu, Y. Haruna, E. Imano, M. Suzuki, T. Kanda, S. Kawano, Oral glucose tolerance test predicts prognosis of patients with liver cirrhosis., Am J Gastroenterol, volume 101, issue 1, pages 70-5, Jan 2006, doi 10.1111/j.1572-0241.2005.00307.x, PMID 16405536
- Diego García-Compeán, Subclinical abnormal glucose tolerance is a predictor of death in liver cirrhosis, World Journal of Gastroenterology, volume 20, issue 22, 2014, pages 7011, ISSN 1007-9327, doi 10.3748/wjg.v20.i22.7011
- http://nutritiondata.self.com/topics/glycemic-index, http://nutritiondata.self.com/topics/glycemic-index, Accessed on 13 February 2016