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Glycemic Index

By: Pharma Tips | Views: 1936 | Date: 29-Jun-2010

Ranking of foods based on their immediate effect on blood glucose (blood sugar) levels is called glycemic index which allows us to rank foods, regarding how quickly they increase blood sugar in the body.

Glycemic Index

Glycemic Index

1. Glycemic index
Ranking of foods based on their immediate effect on blood glucose (blood sugar) levels is called glycemic index which allows us to rank foods, regarding how quickly they increase blood sugar in the body. 
The reference food which is most often white bread is given a value of 100. So, carbohydrate from foods that have a glycemic index below 100 is absorbed more slowly than carbohydrate from bread. Carbohydrate from foods that have a glycemic index above 100 is absorbed more quickly than carbohydrate from white bread.1

Low Glycemic Index List

A. High GI Foods (GI value 70+) 
These carbohydrates cause a rapid rise in blood-glucose levels                                                            
E.g.Glucose/suger-100 ,                                                                  Cornflakes-84 ,                                                                      
Cakes-82 ,                                                                              
B. Medium GI  Foods (GI value 55-69)
                    These carbohydrates cause a medium rise in blood-glucose.
             E.g. Muffin-60,                                                               
              Coco cola-58 ,                                                                   
             Ice cream-61,       
              Boiled rice-64 2  
C. Low GI Carb Foods (GI value 54 or less)
                  These carbohydrates cause a slower rise in blood-sugar
 E.g.- Orange-44,
                       Yogurt-14 ,
                      Oat meal-42 2                                                                                                                                                                                                                                                                                                           

 Glycemic Index does not tell us how many carbohydrates are in a serving of a specific food. This is why Glycemic Load (GL) can be more useful. Glycemic load takes into account the Glycemic index of a food and how many carbohydrates are in a normal serving of that food. To see why this is helpful, we can compare carrots to white pasta.7
Why  Glycemic load  is also important?
Using white bread as the reference food, 50 grams of carrot carbohydrate has a Glycemic index of 131 and 50 grams of pasta carbohydrate has a Glycemic index of 71. This might make us think carrots are an unhealthy food and that they will raise our blood sugar faster than white pasta. However, one whole carrot (a serving) contains only 4 grams of carbohydrate. One cup of pasta (a serving) has 40 grams of carbohydrate. This means that the Glycemic load, which adjusts Glycemic index for serving size, is much lower for carrots.
A serving of carrots has a Glycemic load of 5.2. The Glycemic load for a serving of pasta (1 cup) is very high at 28. In order to have the same Glycemic load from carrots, you would have to eat nearly two pounds of them! This shows how Glycemic index can be misleading. Just because a food has a high Glycemic index, does not mean it will raise blood sugar quickly, when eaten in a normal serving size!

2. Glycemic load.

The Glycemic load (GL) is a ranking system for carbohydrate content in food portions based on their Glycemic index and the portion size. The concept of Glycemic load was developed by scientists to simultaneously describe the quality (Glycemic index) and quantity of carbohydrate in a meal or diet3.

The glycemic load is calculated by Multiply the GI value of a food by the amount of carbohydrate per serving and divides the result by 1003.

Glycemic load   =         Glycemic index × Available Carbohydrate

Spaghetti has a GI value of 40
                            A serving (1 cup) contains 52 grams of carbohydrate. The Glycemic        load of spaghetti is: (40 X 52) divided by 100 = 20.84

Apple has a GI value of 40:-
               A serving (medium size apple) contains 15 grams of carbohydrate. The Glycemic load of an apple is: (40 X 15) divided by 100 = 64 

3. Glycemic index and glycemic load of differenr foods 6

Glycemic index
Glycemic load
High glycemic index (GI>70)
Boiled potato10117
Baked pot8526
Corn flakes8121
Rice cakes7817
Shredded Wheat7515
Cereal bar7719
Water melon724
Moderate glycemic index (GI 56 to 70)
Boiled rice, White6423
Coco cola5816
Fruit cock tail559
Mars bar6526
Ice cream618
Low glycemic index (GI<55)
Sweet corn549
All Brain429
Baked bean487
Orange Juice5013
Boiled spaghetti3818
Kidney bean287
Wheat bread5311
Rye bread415
Potato chip5411
Low fat ice cream503
Plain milk chocolate4312
Skim milk324
Full fat milk273

4. Calculation of Glycemic index


Ten (10) normal subjects are studied on multiple occasions (maximum 3 per week) in the morning after a 10-14hr overnight fast. Subjects are asked to do no unusual vigorous activities on the day before the test, to drink no alcohol and not to smoke for 24h before the test. A drink of the subject's choice is served with each test meal. The subject can chose to have 1-2 cups of water, coffee or tea, with 30ml 2% milk per cup if desired. However, the drink chosen by the subject is the same for every test performed. Test meals are consumed within 10 minutes. 
After a fasting blood sample, subjects eat a test meal and have further blood samples at 15, 30, 45, 60, 90 and 120 minutes after starting to eat. Plasma glucose can be used to determine the glycemic index and gives similar values. However, capillary blood is preferred because it is easier to obtain, the rise in blood glucose is greater than in venous plasma and the results for capillary blood glucose are less variable than those for venous plasma glucose. Thus, differences between foods are larger and easier to detect statistically using capillary blood glucose . An illustration of the difference between glucose as measured in simultaneously-obtained venous plasma and capillary whole blood is shown in Table. 

Glucose response from capillary blood and venous plasma 

0 min15 min30 min45 min60 min90 min120 minIAUC
Capillary blood4.
Venous plasma5.

Capillary blood is obtained by finger-prick and whole blood glucose determined with an automatic analyzer using the glucose oxidase method7.

Standard food 
Either white bread or glucose can be used as the standard food. The GI values obtained if white bread is used are about 1.4 times those obtained if glucose is the standard food. Other standard foods could be used, but to enable comparison with data in the literature, the GI of the new standard food relative to standardized white bread or glucose should be established. 
Same subject 
Blood glucose responses vary considerably from day-to-day within subjects. Thus, to obtain a representative mean response to the standard food, it is recommended that the standard food be repeated at least three times in each subject. This is illustrated by the data in Table given below which is typical for normal subjects. The standard food was repeated three times giving IAUCs of: 114, 155 and 179. The mean ± SD IAUC is 149 ± 33 and the coefficient of variation (100 × SD/mean) is 22%. For this subject, the GI of the test food = 100 × 93/149 = 62. 

Sample blood glucose responses to the ingestion of 50g carbohydrate 
Standard #
Standard #
Standard #
Test Food4.

Incremental area under the curve 
A number of different methods have been used to calculate the area under the curve. For most glycemic index data, the area under the curve has been calculated as the incremental area under the blood glucose response curve (IAUC), ignoring the area beneath the fasting concentration. This can be calculated geometrically by applying the trapezoid rule. When a blood glucose value falls below the baseline, only the area above the fasting level is included. Sample data are shown in Table 1. The data for Standard #1 are used in the diagram in Figure  to illustrate the details of the actual calculation.

Calculations of incremental area under the curve (IAUC) 
The IAUC for the data illustrated above equals the sum of the areas of the triangles and trapezoids: A+B+C+D+E+F 
Area of trephezoites = ½ × (b1+b2) × h
Area of triangle = ½ × b× h

The area of triangle A = 2.0 × 15/2 = 15.0
The area of trapezoid B = (2.0 + 3.6) × 15/2 = 42.0
The area of trapezoid C = (3.6 + 1.0) × 15/2 = 34.5
The area of triangle D = 1.0 × t’/2

Since: t'/15=1.0/(1.0+0.2)
therefore: t' = 15 × 1.0/1.2 = 12.5
therefore the area of triangle D = 1.0 × 12.5/2 = 6.25
The area of triangle E = 0.3 × t"/2
since: t"/30 = 0.3/ (0.3 + 0.2)
therefore: t" = 30 × 0.3/0.5 = 18
therefore the area of triangle D = 0.3 × 18/2 = 2.7
The area of trapezoid F = (0.3 + 0.6) × 30/2 = 13.5
Therefore, IAUC = 15.0 + 42.0 + 34.5 + 6.25 + 2.7 +13.5 = 114 mmol.min/L 8,9

5. Application

Many high-carbohydrate foods common to Western diets produce a high Glycemic response (high-Glycemic-index foods), promoting postprandial carbohydrate oxidation at the expense of fat oxidation, thus altering fuel partitioning in a way that may be conducive to body fat gain.It is also explain as diets too high in carbohydrates (CHOs) lead to high insulin levels which prevent the burning of fat which results in obesity.
Foods that produce the highest blood sugar response Glycemic index (GI), such as carrots, potatoes and parsnips are claimed to be the most dangerous because they are assumed to produce the greatest insulin response
High Glycemic diets can cause excessive calorie-intake and obesity. For example, if we eat a high Glycemic food or a high Glycemic load meal, which by definition triggers a rapid rise in our blood sugar levels, pancreas is over-stimulated and releases a much larger amount of insulin. This large quantity of insulin rapidly mops up the excess sugar in bloodstream causing blood sugar levels to dip quickly below normal, causing to feel hungry once more. 
So even though we may have eaten a high calorie meal, we are induced to feel hungry and eat again within a comparatively short time. This process may lead to excessive calorie intake, weight gain and  possibly causing obesity10.
Both low-fat, high-carbohydrate diets and diets using low-Glycemic index (GI) foods are capable of inducing modest weight loss without specific caloric restriction11.Low Glycemic meal decrease hunger and sub sequently eating. Eating low Glycemic food is important for prevention & treatment of obesity. Low Glycemic food promote fat oxidation. Lowering Carbohydrates or eliminating them will decrease the amount of                  circulating insulin within the plasma. Lowered insulin levels creates an environment in which fat is more readily liberated from there storage sites (adipocytes). 
Basically Insulin is a gate way hormone that actively transports glucose, amino acids and triglycerides (fats) into the various cells of the body including muscle and adipocytes. Considering insulin's main function is to drive nutrients into cells, it would seem obvious that hormones that liberate fat would be suppressed12.
Glycemic index refers to the speed at which carbohydrates are converted by the body into glucose. Glycemic load refers to how fast the carbohydrate is converted into glucose while taking into account the amount of carbohydrate being eaten13.
The possibility that high, long-term intake of carbohydrates that are rapidly absorbed as glucose may increase the risk of type 2 diabetes has been a long-standing         
controversy a high Glycemic load diet can increase the risk of developing type 2 diabetes
Two main mechanisms have been hypothesized14.                                                                                                                                                                                                           
One mediated by increases in insulin resistance and the other by pancreatic exhaustion as a result of the increased demand for insulin.
The body absorbs carbohydrates from different foods at different rates. This leads                         to varying effects on levels of blood glucose and the hormone insulin, which converts glucose into energy.
Foods high on the Glycemic index, such as rice and other simple carbohydrates, cause a rapid spike and then a drop in blood glucose, whereas high-fiber foods tend to be lower on the Glycemic index and have a more gradual effect.
This can contribute to problems with the pancreas (which produces insulin) that may eventually lead to diabetes. In addition, high--Glycemic index foods can directly decrease the body's response to insulin by increasing the production of fatty acids after meals
A high intake of carbohydrates with a high Glycemic index (a relative measure of the incremental glucose response per gram of carbohydrate) produced greater insulin resistance than did the intake of low-Glycemic-index carbohydrates. both the Glycemic index and the Glycemic load (the Glycemic index multiplied by the amount of carbohydrate) of the overall diet have been associated with a greater risk of type 2 diabetes in both men and women15.
A higher intake of cereal fiber has been consistently associated with lower diabetes risk. replacing high-Glycemic-index carbohydrates with a low-Glycemic-index forms will improve Glycemic control and, among persons treated with insulin, will reduce hypoGlycemic episodes16.
Coronary heart  disease
A diet high in carbohydrates with high Glycemic indexes (GI) and Glycemic load were linked to risk of coronary heart disease development in women in a large prospective study. Hyperglycemia and hyperinsulinemia are central features of the metabolic syndrome and type 2 diabetes mellitus, which contribute to the pathogenesis of coronary heart disease (CHD).
In a tightly controlled study of patients with type 2 diabetes, serum total cholesterol, LDL cholesterol, and Apo lipoprotein B concentrations fell more significantly after a low-GI diet than after a high-GI diet.
Glycemic index (a measure of the postprandial Glycemic potential of carbohydrates) and Glycemic load (average Glycemic index x amount of carbohydrate) predicts coronary infarct and cardiovascular disease risk factors, including HDL cholesterol, triglycerides and C-reactive protein17.
In short-term intervention studies of overweight and Hyperlipidemia patients, low Glycemic index diets lead to improvements in cardiovascular disease risk factors, including reduced LDL cholesterol and improved insulin sensitivity, as well as greater body fat loss on energy-restricted diets dietary GI and/or Glycemic load independently predict cardiovascular disease, with relative risk ratios of 1.2 to 1.7comparing highest and lowest quintiles.
A diet containing low GI carbohydrate significantly reduces your risk of heart disease. decreasing dietary GL by reducing the intake of high-Glycemic beverages and replacing refined grain products and potatoes with minimally processed plant-based foods such as whole grains, fruits, and vegetables may reduce CHD incidence in sedentary individuals and populations with a high prevalence of overweigh 
Sport performance
There are times when low G.I. foods provide an advantage and times when high G.I. foods are better. For best performance a serious athlete needs to learn about which foods have high and low G.I. factors and when to eat them. 
The carbohydrate we eat is stored in the body in the form of Glycogen in the muscles and in the liver.
A small amount circulates as glucose in the blood. When exercising at high intensities the main fuels are blood glucose and muscle glycogen. The body also can use fats at low intensities but loses this ability when high intensity is required. The bigger your stores of glucose and glycogen, the longer an athlete can exercise before fatigue sets in. Maintaining high glycogen stores is the key to maintaining quality training performance on a daily basis18.
Hyperinsulinemia is implicated in the development of colorectal cancer, determinants of serum insulin levels, like the Glycemic load and the Glycemic index of the diet, could influence cancer risk. 
High-carbohydrate foods such as soft drinks, crackers, breads, cookies, pastries, potato chips, pastas, desserts, granola bars, "energy" drinks and the like. These products are all now linked to cancer,
Diets with high Glycemic loads -- that is, diets rich in processed foods like white  bread, white rice and other foods made from refined grains (cakes, cookies, chips, etc.) as well as other high-Glycemic foods like potatoes and corn -- were associated with increased risk of colorectal cancer. The carbohydrates at the lower end of the Glycemic scale, such as vegetables and products made from whole grains, were not associated with increased risk.
The higher their value, the greater the glucose and insulin responses. Raised insulin levels are associated with19.
Endometrial Cancer
The odds ratios (OR) of endometrial cancer, after adjustment for major risk factors, for the highest versus the lowest quintile of dietary GI and GL were 2.1 (95% confidence interval [CI] = 1.4-3.2) and 2.7 (95% CI = 1.8-4.2), respective consumption of carbohydrates with high dietary Glycemic index would predict risk of postmenopausal 19
Breast Cancer 
Associations between carbohydrate intake and breast cancer incidence were analyzed using Cox's regression models.
 There was no association for intake of glucose, fructose, sucrose, maltose, lactose, or starch and breast cancer incidence rate, and no association for Glycemic index or Glycemic load after adjusting for confounding factors. 
Intake of different carbohydrates was not associated with breast cancer incidence rates for either estrogen receptor positive (ER+) or (ER-) breast cancer. 
Similarly, Glycemic index and Glycemic load were not associated with ER+ breast cancer after adjusting for confounding factors. A borderline significant positive association between Glycemic index and (ER-) breast cancer was observed (P = 0.05)20.
Polycystic ovarian syndrome (PCOS)
PCOS is the most common cause of infertility in women of childbearing age Polycystic ovarian syndrome (PCOS) is an endocrinologic disorder that can appear in women of reproductive age. It is the leading cause of fertility and affects 6-10% of women of childbearing age. It is referred to as a syndrome because it contains many symptoms. These symptoms include obesity, hirsutism, acne, infrequent or abnormal ovulation, amenorrhea, oligominorrhea, hyperandrongenism, an elevated utilizing hormone to follicle stimulating hormone ratio, chronic pelvic pain, insulin resistance, hyperinsulinemia, type II diabetes, dyslipidemia, and hypertension. These symptoms can get worse with weight gain. Women with PCOS have an increased risk for developing type II diabetes, high cholesterol and triglyceride levels, cardiovascular disease, endometrial cancer, and insulin resistance. Of these disease the most common is insulin resistance and type II diabetes21.
The cause of PCOS 
Foods high in carbohydrates (starches and sugars) are most likely to increase blood sugar. As increase the sugar level in response to it insulin level also increase.
The insulin builds up in the body, which is hyperinsulinemia, and causes ovarian cells to secrete androgens and decrease sex hormone binding hormone globulin (SHBG). The interacting of insulin and hormones lead to symptoms of PCOS. Some literature suggest it is genetic with autonomic dominant mode of transmission.
Treatment of  PCOS
First line treatment is lifestyle changes. If a woman is overweight she is encouraged to lose weight as this aids in the return of ovulation and decreases other symptoms.
It is thought that by losing weight, the elevated insulin is reduced and this would result in a decrease in ovarian androgen production. Weight loss also reduces a woman's risks of developing diabetes and cardiovascular disease. 
The Glycemic Index is relevant for women who have PCOS (polycystic ovary syndrome). The Glycemic Index is a ranking of foods by how much they increase your blood sugar levels 2-3 hours after you eat them. Foods high in carbohydrates (starches and sugars) are the ones you'll find in the index, because they're most likely to increase your blood sugar. Chronically high insulin is a problem for women with PCOS, because insulin profoundly alters overall hormone balance, and causes your metabolism to go awry.
A requirement for controlling polycystic ovarian syndrome is to dampen your insulin response after food or drink is consumed. intakes of high-GI carbohydrates (like sweets, white bread, white rice) cause elevated levels of glucose and insulin. By restricting these high-GI carbs, a low-GI weight loss plan is particularly effective for PCOS patients who are prone to fat storage as a result of their inability to metabolize carbohydrates.

1.  Brand-Miller J, Barclay AW, Irwin T. A new food labeling program for the glycemic index. Proc Nutr Soc Aust 2001;25:S .                                                                                
2. Foster-Powell, Ket al. International table of glycemic index and glycemic loadvalues. Am J Clin Nutr.76 (1): 5-56, 2. 
3. Wolever TMS, Jenkins DJA, Jenkins AL, Josse RG. The glycemic index: methodology and clinical implications. Am J of Clin Nutr 1991;54:846-54.    
4. Wolever TMS. Effect of blood sampling schedule and method calculating the area under the curve on validity and precision of glycaemic index values. Brit J of Nutr. 2004;91:295-300.
5. Wolever TMS, Jenkins DJA, Josse RG, Wong GS, Lee R. The glycemic index: similarity of values derived in insulin-dependent and non-insulin dependent diabetic patients. J Am Coll Nutr 1987;6:29. 
6. Ludwig,DS.The glycemic index: physiological mechanisms relating to obesity, diabetes, and cardiovascular disease.JAMA.287 (18): 2414-2423, 2002.002.
7. Augustin LS, Gallus S, Bosetti C, Levi F, Negri E, Franceschi S, Dal Maso L, Jenkins     DJ, Kendall CW, La Vecchia C. Glycemic index and glycemic load in endometrial cancer. Int J Cancer. 2003;105(3):404-407.
8.  Augustin LS, Dal Maso L, La Vecchia C, Parpinel M, Negri E, Vaccarella S, Kendall CW, Jenkins DJ, Francesch S. Dietary glycemic index and glycemic load, and breast cancer risk: A case-control study. Ann Oncol. 2001;12 (11):1533-1538.
 9. Ornish, Dean et al. Intensive lifestyle changes may affect the polycystic ovarian syndrom.  J Urology2005 174:1065. 
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