Obesity and diabetes are increasingly costly problems in Western countries, both in terms of individual health impacts and expenditures of health-care dollars. According to an article in the July 29, 2009, issue of "Health Affairs," the annual monetary cost of obesity alone in the United States totals nearly 150 billion dollars. Dietary education, including an understanding of glycemic index and glycemic load, plays an important role in managing these conditions.
Carbohydrates and Blood Glucose
Dietary carbohydrates include starches, most fiber-containing foods and sugars, such as glucose, fructose and sucrose. During digestion, carbohydrates are broken down into sugars of varying complexity. Some of these sugars can be absorbed intact through the intestinal wall, but the final product of carbohydrate digestion is glucose, the major fuel for your body's cells. Carbohydrates that contain simpler sugars are more readily digested and assimilated. Since simple sugars are absorbed more rapidly, they induce a faster rise in your blood glucose level.
Simple vs. Complex Carbohydrates
Simple dietary sugars, such as glucose and sucrose, do not require extensive digestion before they are assimilated. Polysaccharides, which are complex sugars found in starches, grains and cellulose, are not as easily digested as simple sugars. Hence, they are absorbed more slowly from your intestine and consequently do not cause your blood glucose to "spike" like simple sugars do.
Blood Glucose and Insulin
Insulin is a hormone produced by specialized cells in your pancreas, which is an organ that lies directly behind your stomach. One of insulin's primary roles is to facilitate the uptake of glucose from your bloodstream into your individual cells, where it can be used for energy. Whenever you eat a meal that contains carbohydrates, your pancreas releases insulin to "push" the glucose from that meal into your cells. The faster your blood glucose increases, the faster your insulin level rises.
Glycemic Index
A 2006 article in "American Family Physician" defines glycemic index as a measure of how much a given food raises your blood sugar in the first two hours after you eat it. The more rapidly a carbohydrate is absorbed into your bloodstream as glucose, the higher its glycemic index. Reference foods, arbitrarily scored at 100, include glucose and white bread, since they are easily digested and absorbed. Other carbohydrates are rated according to how they compare to the reference foods. A glycemic index of 70 or above is considered high, while indexes of 56 to 69 and 55 or under are considered medium and low, respectively.
Glycemic Load
Glycemic index compares the potential of equal amounts of different carbohydrates to raise your blood sugar. However, the total physiologic burden of a meal is also dependent on the amount of carbohydrate consumed. Glycemic load is a more accurate measure of this parameter. It is calculated by multiplying the food's glycemic index by the amount of carbohydrate, in grams, in the portion consumed and dividing the total by 100. According to the Linus Pauling Institute, glycemic load better defines the total impact of carbohydrates in your diet.
Implications
Glycemic index and glycemic load are useful concepts for managing either diabetes or obesity. Diabetics who don't control their blood sugars are more likely to develop complications, such as blindness, amputations and heart disease. Foods with a high glycemic index or load are more likely to elevate blood glucose to dangerous levels. Overweight individuals can also exploit these principles. High-glycemic-index foods generate an insulin surge that eventually drives your blood glucose lower than it would normally fall. This stimulates your appetite, which, in turn, prompts increased caloric intake.
