The glycemic index ranks carbohydrates, and foods that contain carbohydrates, according to their ability to raise blood sugar levels. Only carbohydrate-containing foods are ranked, because carbohydrates are readily converted into glucose by your body. Eating foods that are low on the GI may help control or prevent insulin resistance, type 2 diabetes, heart disease, high blood pressure and high cholesterol.
Understanding the Glycemic Index
The glycemic index, or GI, is a system that ranks the potential of a food to raise your blood sugar level, relative to pure glucose. Pure glucose is arbitraily assigned a score of 100; foods that score below 55 are considered low-GI foods, foods that score between 55 and 69 are medium-GI foods and foods that score above 70 are considered high-GI foods and will rapidly spike your blood sugar. Many popular diets, such as the South Beach Diet and the Zone are based on choosing the "right" carbohydrates -- low-GI carbs that have little impact on your blood sugar.
The GI Testing Process
Glycemic index testing is done at SUGiRS, the Sydney University GI Research Service in Sydney, Australia. A group of at least 10 healthy individuals are fed 50 g of the carbohydrate being tested and then they have their blood sugar levels tested at regular intervals over a two-hour period. A few days later the same individuals consume 50 g of pure glucose and have their blood sugar levels tested at the same timed intervals. Each individual's response is calculated by dividing their blood sugar levels after consuming the test food by their blood sugar levels after having pure glucose. Then all of the responses are averaged to determine a food's GI value. Only whole foods, not single ingredients, are tested because real people have to eat the food being tested. That's why flour can't be tested and assigned a rank on the GI but pasta and bread can be.
Why the Glycemic Index is Important
The GI was originally developed to help people with insulin resistance and diabetes make carbohydrate choices that would have the smallest effect on their blood sugar levels. By avoiding a sudden spike in blood sugar levels, diabetics could control glucose levels more effectively and avoid some of the serious health consequences associated with chronic high blood sugar, such as kidney failure, blindness and nerve damage. Eating foods low on the GI can also help you feel full longer and decrease appetite, which may lead to eating less often and consuming fewer calories -- resulting in weight loss. According to the Linus Pauling Institute, people following low-GI diets reduce their risk of cardiovascular disease, since high-GI diets are associated with high triglyceride and low HDl, or "good" cholesterol levels.
Not All Low-GI Foods Are Healthy Foods
Carbohydrates may raise your blood sugar, but fat, fiber and protein slow your body's conversion of sugar into glucose. So foods high in carbs that are also high in protein, fat or fiber, may score low on the glycemic index. A Snickers bar, with its high fat content, is a low-GI food, with a score of 40 but a mango is a medium-GI food with a score of 56. Don't choose foods based solely on their GI ranking; it's important to consider the nutrient density of the foods you eat. The mango has a wealth of essential vitamins that no candy bar can match.
