Understanding the Glycemic Index
January 7, 2013
By Brittany Sinensky, B.S., B.S.
Over three decades ago, Dr. David J. Jenkins introduced the glycemic index (GI). It's a measure of how quickly blood sugar rises when you eat particular foods. Since then, the GI has become an effective treatment tool for people with diabetes.
More recently, health care professionals are using the GI and the newer glycemic load (GL) to help prevent or treat other chronic diseases. These include cardiovascular disease and cancer.
In the world of nutrition information overload today, many people are wondering if the GI is the new gold standard for helping people make good dietary choices even healthy people.
The GI measures exactly how quickly or slowly carbohydrates (sugars and starch) are digested. Foods are assigned a number by measuring their effect on blood sugar. This is done in a laboratory.
The GL also is a number. It takes into account how much carbohydrate gets into the bloodstream and how quickly it gets there. The GL is estimated by multiplying the food's GI value by the number of grams of available carbohydrate in a specific serving size of a food and dividing by 100.
The GI and GL values help people manage their glycemic response (rise or fall of blood sugar) after eating certain foods. Foods with a high glycemic index or load will cause a greater glycemic response than foods with a low GI or GL.
Some foods, such as watermelon, have a high GI (72), but a low GL (4). That's because a realistic serving size lowers the effect that watermelon has on raising blood sugar.
Here are the GI and GL for common foods:
How a food affects blood sugar is not just important for people with diabetes. According to research, it's also important for people with other chronic diseases, such as cardiovascular and cancer. A meta-analysis in 2008 found that diets with a high GI or GL independently increased the risk of:
The study provides strong evidence that diets with a high GI, high GL or both, increase the risk of chronic lifestyle-related diseases.
The GI can also help people who are overweight or obese lose weight. Studies show that people lost more weight on a low GI diet than on high GI or popular calorie-restricted diets. People also maintain their weight losses better when eating a diet moderately high in protein and low in GI.
For many, a diet based on GI and/or GL may seem difficult to follow. That's because:
However, despite these drawbacks, there is overwhelming evidence that everyone could benefit from following a low-GI and/or low-GL diet. In fact, it may be easier to stick to a diet using the GI and/or GL as a guideline than trying to stick to a stringent diet in which you can only eat certain foods. Also, there don't seem to be any safety concerns in adopting this diet.
Here are some tips to use when using the GI or GL to help you make food choices:
Barclay, A.W., Petocz, P., et al. "Glycemic index, glycemic load, and chronic disease risk A meta-analysis of observational studies." The American Journal of Clinical Nutrition. 2008; 87: 627-637.
Brittany Sinensky is a dietetic intern at Brigham and Women's Hospital in Boston, MA. She holds a Bachelor of Science in Marketing from Providence College and a Bachelor of Science in Nutrition from Long Island University.