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Encyclopedia > Glycemic Index

Glycemic index (also glycaemic index, GI) is a ranking system for carbohydrates based on their effect on blood glucose levels. It compares carbohydrates gram for gram in individual foods, providing a numerical, evidence-based index of postprandial (post-meal) glycemia. The concept was invented by Dr. David J. Jenkins and colleagues in 1981 at the University of Toronto. Lactose is a disaccharide found in milk. ... In medicine, blood sugar is glucose in the blood. ... Glycemia is the concentration of glucose in the blood. ... David JA Jenkins (MD, PhD, DSc) is Professor of Nutritional Sciences at the University of Toronto, Canada. ... The University of Toronto (U of T) is a coeducational public research university in Toronto, Ontario, Canada. ...


Carbohydrates that break down rapidly during digestion have the highest glycemic indices. Carbohydrates that break down slowly, releasing glucose gradually into the blood stream, have a low glycemic index. A lower glycemic index suggests slower rates of digestion and absorption of the sugars and starches in the foods and may also indicate greater extraction from the liver and periphery of the products of carbohydrate digestion. A lower glycemic response is often thought to equate to a lower insulin demand, better long-term blood glucose control and a reduction in blood lipids. But in fact, some foods having a low glycemic index or having very little carbohydrate cause a high insulin response or raise blood lipids. The insulin index may therefore also be useful as it provides a direct measure of the insulin response to a food. This article or section does not cite any references or sources. ... Insulin (from Latin insula, island, as it is produced in the Islets of Langerhans in the pancreas) is a polypeptide hormone that regulates carbohydrate metabolism. ... The Insulin Index is a measure used to quantify the amount of insulin response of various foods. ...


The glycemic index of a food is defined by the area under the two hour blood glucose response curve (AUC) following the ingestion of a fixed portion of 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. area under the curve: AUC means area under the curve. This is the area under the concentration time curve. ...

The effect on blood glucose from a high versus low glycemic index carbohydrate

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.[1] Image File history File links Glycemic. ... Image File history File links Glycemic. ...


The current validated methods use glucose as the reference food, giving it a glycemic index value of 100 by definition. This has the advantages in that it is universal and it results in maximum GI values of approximately 100. White bread can also be used as a reference food, giving a different set of GI values (if white bread = 100, then glucose ≈ 140). For people whose staple carbohydrate source is white bread, this has the advantage of conveying directly whether replacement of the dietary staple with a different food would result in faster or slower blood glucose response. The disadvantages with this system are that the reference food is not well-defined, and the GI scale is culture dependent. This article or section does not cite any references or sources. ...

Contents

Glycemic index of foods

GI values can be interpreted intuitively as percentages on an absolute scale and are commonly interpreted as follows:

Classification GI range Examples
Low GI 55 or less most fruit and vegetables (but not root vegetables), oats, buckwheat, whole barley, All-bran, Basmati rice
Medium GI 56 - 69 sucrose, Mars bar, croissant
High GI 70 or more corn flakes, baked potato, Jasmine rice, white bread

A low GI food will release glucose more slowly and steadily. A high GI food causes a more rapid rise in blood glucose levels and is suitable for energy recovery after endurance exercise or for a person with diabetes experiencing hypoglycemia. Basmati rice, (basmati apparently means Queen of fragrance in the Hindi language) is a small long-grained variety of rice, famous for its fragrance and delicate flavour. ... Jasmine rice (Thai: ; kao hom mali) is a long-grain variety of rice that has a nutty aroma and subtle flavor. ... Hypoglycemia (hypoglycæmia in the UK) is a medical term referring to a pathologic state produced by a lower than normal level of sugar (glucose) in the blood. ...


The glycemic effect of foods depends on a number of factors such as the type of starch (amylose vs. amylopectin), physical entrapment of the starch molecules within the food, fat content of the food and increased acidity of the meal — adding vinegar for example, will lower the GI. The presence of fat or soluble dietary fibre can inhibit carbohydrate absorption, thus lowering the GI. Unrefined breads with higher amounts of fibre generally have a lower GI value than white breads, but, while adding butter or oil will lower the GI of bread, the GI ranking does not change. That is, with or without additions, there is still a higher blood glucose curve after white bread than after a low GI bread such as pumpernickel. Many brown breads, however, are treated with enzymes to soften the crust, which makes the starch more accessible. This raises the GI, with some brown breads even having GI values over 100. Starch (CAS# 9005-25-8) is a complex carbohydrate which is insoluble in water; it is used by plants as a way to store excess glucose. ... Amylose (CAS# 9005-82-7) is a linear polymer of glucose linked with mainly α(1→4) bonds. ... Amylopectin is a highly branched polymer of glucose found in plants. ... Vinegar is sometimes infused with spices or herbs—as here, with oregano. ... Dietary fibers are the indigestible portion of plant foods that move food through the digestive system, absorbing water. ... Lactose is a disaccharide found in milk. ... Pumpernickel is a type of German sourdough bread made with a combination of rye flour and rye meal (a more coarsely ground form of the flour). ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ...


The glycemic index can only be applied to foods with a reasonable carbohydrate content, as the test relies on subjects consuming enough of the test food to yield about 50 g of available carbohydrate. Many fruits and vegetables (but not potatoes) contain very little carbohydrate per serving, or have very low GI values. This also applies to carrots, which were originally and incorrectly reported as having a high GI.[2] Alcoholic beverages have been reported to have low GI values, however it should be noted that beer has a moderate GI. Recent studies have shown that the consumption of an alcoholic drink prior to a meal reduces the GI of the meal by approximately 15%.[3]


Disease prevention

Several lines of recent scientific evidence have shown that individuals who followed a low GI diet over many years were at a significantly lower risk for developing both type 2 diabetes and coronary heart disease than others, but the results obviously depend on the two diets being compared. High blood glucose levels or repeated glycemic "spikes" following a meal may promote these diseases by increasing oxidative damage to the vasculature and also by the direct increase in insulin levels. [4] In the past, post-meal hyperglycemia has been a risk factor mainly associated with diabetes, however more recent evidence shows that postprandial hyperglycemia presents an increased risk for atherosclerosis in the non-diabetic population.[5] This article is about the disease that features high blood sugar. ... Insulin (from Latin insula, island, as it is produced in the Islets of Langerhans in the pancreas) is a polypeptide hormone that regulates carbohydrate metabolism. ... Hyperglycemia or High Blood Sugar is a condition in which an excessive amount of glucose circulates in the blood plasma. ... Look up Postprandial in Wiktionary, the free dictionary. ...


On the other hand there are regions, such as Peru and Asia, where people eat high-glycemic index foods such as potatoes and rice, but without a high level of obesity or diabetes. The high consumption of legumes in South America and fresh fruit and vegetables in Asia likely has a lowering glycemic effect in these individuals. The mixing of high and low GI carbohydrates produces moderate GI values. Varieties of soybean seeds, a popular legume The term legume has two closely related meanings in botany, a situation encountered with many botanical common names of useful plants whereby an applied name can refer to either the plant itself, or to the edible fruit (or useful part). ...


The glycemic index is supported by leading international health organisations including the American Diabetes Association.[6]


Weight control

Recent animal research provides compelling evidence that high GI carbohydrate is associated with increased risk of obesity. In human trials, it is typically difficult to separate the effects from GI and other potentially confounding factors such as fibre content, palatability, and compliance. In the study (Pawlak et al, 2004), male rats were split into high and low GI groups over 18 weeks while mean bodyweight was maintained. Rats fed the high GI diet were 71% fatter and had 8% less lean body mass than the low GI group. Postmeal glycemia and insulin levels were significantly higher and plasma triglycerides were three-fold greater in the high GI fed rats. Furthermore, pancreatic islet cells suffered "severely disorganised architecture and extensive fibrosis". The evidence in this study showed that continued consumption of high glycemic index carbohydrates would likely have led to the development of severe metabolic abnormalities. Glycemia is the concentration of glucose in the blood. ... Insulin (from Latin insula, island, as it is produced in the Islets of Langerhans in the pancreas) is a polypeptide hormone that regulates carbohydrate metabolism. ... Triglyceride (blue: fatty acid; red: glycerol backbone) Triglycerides are glycerides in which the glycerol is esterified with three fatty acids. ... A porcine islet of Langerhans. ... Fibrosis is the formation or development of excess fibrous connective tissue in an organ or tissue as a reparative or reactive process, as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue. ... Santorio Santorio (1561-1636) in his steelyard balance, from Ars de statica medecina, first published 1614 Metabolism (from μεταβολισμος(metavallo), the Greek word for change), in the most general sense, is the ingestion and breakdown of complex compounds, coupled...


Endurance Athletes

Endurance athletes such as ultra-marathoners and iron man triathletes have become increasingly aware of the glycemic index of foods taken before and during training and competition. In the hours before a competition athletes may consume foods with a lower GI value so that energy is released more slowly. During competition, the athlete may try to balance the consumption of high and low glycemic index foods to maintain constant energy levels and avoid "energy spikes".


Criticism

The glycemic index has been criticised for the following reasons:

  • The GI does not take into consideration other factors besides glycemic response, such as insulin response.
  • The GI of a food varies depending on the kind of food, its ripeness, the length of time it was stored, how it was cooked, its variety (potatoes from Australia, for example, have a much higher GI than potatoes from the United States[citation needed]), and how it was processed or manufactured.
  • The GI of a food varies from person to person and even in a single individual from day to day, depending on blood glucose levels, insulin resistance, and other factors.
  • The GI of a mixed meal can be difficult to predict. For example, fats and proteins can make a meal sit in the stomach longer, which reduces a food's GI.
  • The GI value is based on a portion that contains 50 grams of carbohydrate only. This criticism can be addressed by taking the Glycemic load into account.

Binomial name Solanum tuberosum L. The potato (Solanum tuberosum) is a perennial plant of the Solanaceae, or nightshade, family, grown for its starchy tuber. ... Insulin resistance is the condition in which normal amounts of insulin are inadequate to produce a normal insulin response from fat, muscle and liver cells. ... The glycemic load (GL) is a ranking system for carbohydrate content in food portions based on their glycemic index (GI) and the portion size. ...

See also

// Note: As far as fruits go, if it tastes too sweet its generally safe to assume that it has an elevated GI. apples (40) banana (51) Ok Green blueberries (40) Fresh cherries (22) grapefruit (25) green grapes (43) orange (51) pears (33) plums (24) prunes (29) raspberries tomatoes asparagus... The glycemic index pyramid is a pyramid-shaped guide to eating foods, as determined by their glycemic index. ... The glycemic load (GL) is a ranking system for carbohydrate content in food portions based on their glycemic index (GI) and the portion size. ... The diet recommended for people who suffer from diabetes mellitus is one that is high in dietary fibre, especially soluble fibre, but low in fat (especially saturated fat) and sugar. ... The Insulin Index is a measure used to quantify the amount of insulin response of various foods. ... Glycemic Index The Glycemic Index (also glycaemic index, GI) is a ranking system for carbohydrates based on their immediate effect on blood glucose levels. ...

References

  1. ^ Brouns et al (2005). "Glycaemic index methodology." Nutrition Research Reviews 18; 145-171
  2. ^ Brand-Miller et al (2005). The Low GI Diet Revolution: The Definitive Science-based Weight Loss Plan. Marlowe & Company. New York, NY
  3. ^ Brand-Miller, in press
  4. ^ Temelkova-Kurktschiev et al (2000). "Postchallenge plasma glucose and glycemic spikes are more strongly associated with atherosclerosis than fasting glucose or HbA1c level." Diabetes Care 2000 Dec;23(12):1830-4
  5. ^ Balkau et al (1998) "High blood glucose concentration is a risk factor for mortality in middle-aged nondiabetic men. 20-year follow-up in the Whitehall Study, the Paris Prospective Study, and the Helsinki Policemen Study." Diabetes Care 1998 Mar;21(3):360-7
  6. ^ Sheard et al (2004). "Dietary carbohydrate (amount and type) in the prevention and management of diabetes: a statement by the american diabetes association." Diabetes Care;27(9):2266-71
  • DJ Jenkins et al (1981). "Glycemic index of foods: a physiological basis for carbohydrate exchange." Am J Clin Nutr 34; 362-366
  • Pawlak et al (2004). "Effects of dietary glycaemic index on adiposity, glucose homoeostasis, and plasma lipids in animals." Lancet 28;364(9436):778-85

External links


  Results from FactBites:
 
Linus Pauling Institute at Oregon State University (1605 words)
To determine the glycemic index of a food, volunteers are typically given a test food that provides 50 grams of carbohydrate and a control food (white bread or pure glucose) that provides the same amount of carbohydrate on different days (2).
The glycemic index is calculated as the area under the glucose curve after the test food is eaten, divided by the corresponding area after the control food is eaten.
The glycemic load of a food is calculated by multiplying the glycemic index by the amount of carbohydrate in grams provided by a food and dividing the total by 100 (1).
Glycemic index - definition of Glycemic index in Encyclopedia (425 words)
Glycemic index values for different foods are calculated by comparing measurements of their effect on blood glucose compared with a reference food.
The glycemic effect of white bread depends on factors such as flour variations, and is of little interest to people whose staple is (for example) rice, corn, or millet.
Glycemic index is also not particularly well correlated with the measures of insulin response.
  More results at FactBites »

 
 

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