Not all carbohydrate foods are created equal impact, in fact they behave quite differently in our bodies. The glycemic index or GI describes this difference by ranking carbohydrates according to their effect on our blood glucose levels. Choosing low GI carbohydrates that produce only small fluctuations in our blood glucose and insulin levels is the secret to long-term health reducing our risk of heart disease and diabetes and is the key to sustainable weight loss.
The Glycaemic Index (GI) categorizes starchy foods according to their potential to raise the blood glucose levels. Blood glucose levels fluctuate following ingestion of foods containing carbohydrates. GI measures the effects of carbohydrates on blood glucose levels by serving either a 50 g or a 25 g available carbohydrate portion (which may or may not be the normal serving size).
GI = IAUC of test food x 100
IAUC of standard
According to the GI values obtained with glucose as the standard, foods are categorized as low, medium or high GI foods.
Low GI = 55 or less Medium GI = 56-69 High GI = 70 or above
Glycaemic Load
As GI is estimated with a standard amount of carbohydrate load which may or may not be the normal serving size, glycaemic load (GL) was introduced to apply the GI concept to the normal serving sizes of foods (edible portions).
Glycaemic load is calculated as,
GL = [GI x amount of carbohydrate (grams) in
the edible portion]
100
Thus, high GI/low carbohydrate diets or low GI/high carbohydrate diets can have the same GL.
According to the glycaemic load values foods can be categorized as given below (with reference to glucose):
Low GL = 10 or less Medium GL = 11-19 High GL = 20 or more
High GI foods - Carbohydrates are digested fast. Thus, glucose is released into the blood rapidly.
Low GI foods – Glucose is released slowly into blood stream.
Foods with low GI are reported to reduce the risk of diabetes and coronary heart disease and maintain a healthy body weight. The high glycaemic responses resulting from high GI foods can be lowered by consuming high GI foods with low or medium GI foods. Ex. Bread or high GI rice with curries made with low GI foods.
Measuring the Glycemic Index of Foods
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. Blood samples for the determination of glucose are taken prior to eating and at regular intervals after eating over the next several hours.
The changes in blood glucose over time are plotted as a curve. 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 value is multiplied by 100 to represent a percentage of the control food.
For example, a baked potato has a glycemic index of 76 relative to glucose and 108 relative to white bread, which means that the blood glucose response to the carbohydrate in a baked potato is 76% of the blood glucose response to the same amount of carbohydrate in pure glucose and 108% of the blood glucose response to the same amount of carbohydrate in white bread.
In contrast, cooked brown rice has a glycemic index of 55 relative to glucose and 79 relative to white bread. In the traditional system of classifying carbohydrates, both brown rice and potato would be classified as complex carbohydrates despite the difference in their effects on blood glucose levels.
Diabetes mellitus type 1 (Type 1 diabetes, IDDM, or, obsoletely, juvenile diabetes) is a form of diabetes mellitus that results from autoimmune destruction of insulin-producing beta cells of the pancreas. The subsequent lack of insulin leads to increased blood and urine glucose. The classical symptoms are polyuria (frequent urination), polydipsia (increased thirst), polyphagia (increased hunger), and weight loss.
Type 1 diabetes is fatal unless treated with insulin. Injection is the most common method of administering insulin; insulin pumps and inhaled insulin have been available at various times. Pancreas and islet transplants have been used to treat type 1 diabetes; however, islet transplants are currently still at the experimental trial stage.
Diabetes mellitus type 2 – formerly non-insulin-dependent diabetes mellitus (NIDDM) or adult-onset diabetes – is a metabolic disorder that is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency. Diabetes is often initially managed by increasing exercise and dietary modification. If the condition progresses, medications may be needed.
Type 2 Diabetes Mellitus
High dietary glycemic loads have been associated with an increased risk of developing type 2 diabetes mellitus (DM) in several large prospective studies. In the Nurses’ Health Study (NHS), women with the highest dietary glycemic loads were 37% more likely to develop type 2 DM over a 6-year period than women with the lowest dietary glycemic loads. Additionally, women with high-glycemic load diets that were low in cereal fiber were more than twice as likely to develop type 2 DM than women with low-glycemic load diets that were high in cereal fiber.
The results of the Health Professionals Follow-up Study (HPFS), which followed male health professionals over six years were similar. In the NHS II study, a prospective study of younger and middle-aged women, those who consumed foods with the highest glycemic index values and the least cereal fiber were also at significantly higher risk of developing type 2 DM over the next eight years.
The foods that were most consistently associated with increased risk of type 2 DM in the NHS and HPFS cohorts were potatoes (cooked or French-fried), white rice, white bread, and carbonated beverages.The Black Women's Health study, a prospective study in a cohort of 59,000 U.S. black women, found that women who consumed foods with the highest glycemic index values had a 23% greater risk of developing type 2 DM over eight years of follow-up compared to those who consumed foods with the lowest glycemic index values.
In the American Cancer Society Cancer Prevention Study II, which followed 124,907 men and women for nine years, high glycemic load was associated with a 15% increased risk of type 2 DM. Further, in a cohort of over 64,000 Chinese women participating in the Shanghai Women's Health Study, high glycemic load was associated with a 34% increase in risk of type 2 DM; this positive association was much stronger among overweight women.
A U.S. ecological study of national data from 1909 to 1997 found that increased consumption of refined carbohydrates in the form of corn syrup, coupled with declining intake of dietary fiber, has paralleled the increase in prevalence of type 2 DM. Today, high-fructose corn syrup (HFCS) is used as a sweetener and preservative in many commercial products sold in the United States, including soft drinks and other processed foods.
To make HFCS, the fructose content of corn syrup (100% glucose) has been artificially increased; common formulations of HFCS now include 42%, 55%, or 90% fructose. When consumed in large quantities on a long-term basis, HFCS is unhealthful and may contribute to other chronic diseases besides type 2 DM, including obesity and cardiovascular disease.
http://www.diabetesnet.com
http://www.whfoods.com
http://lpi.oregonstate.edu
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