What’s the Deal with Glycemic Index?
If there’s one fad I have always hated as a dietitian, it is glycemic index. I recently had a local paper ask me to answer some questions about it. The glycemic index (GI) has been used as a basis for popular diets like South Beach and The Zone. This has made it a very popular discussion. Glycemic Index is nothing more than a measure of how quickly a carbohydrate-containing food causes our blood sugar levels to rise. Food is ranked on a scale of 0 to 100 (in comparison to a reference food- glucose (sugar) or white bread). There are Low, Medium and High GI foods.
High glycemic index foods (GI ranking of 70 or more) are quickly digested and absorbed (white bread, bagels, corn flakes, puffed rice, instant oatmeal, white rice, Russet potatoes, pretzels and rice cakes). High GI foods cause a rapid rise in blood sugar. Foods with a low glycemic index are digested and absorbed at a slower rate; this causes a slower rise in blood sugar. Foods with a lower GI contain more fiber, protein and or fat. Low GI foods (GI ranking of 55 or less) include: many whole grain breads and cereals, (whole wheat bread, oatmeal: rolled or steel-cut, barley, bulgar), Greek yogurt, peanuts, legumes and lentils, most fruits, all non-starchy vegetables and some starchy vegetables like sweet potatoes. Medium GI foods (GI ranking of 56-69) include: quick oats, couscous, whole wheat, rye and pita bread and brown, wild, or basmati rice. Meats and fats don’t contain carbohydrates and therefore, do not have a GI.
GI isn’t a perfect system, but it can be another useful tool for making healthier food choices and as tool to manage blood glucose levels in people with diabetes. The down side to using GI as a guide- it can be complicated and many factors affect a food’s glycemic index: ripeness and storage time, degree of processing, or length of cooking time. Also, the GI ranking only applies when a food is consumed on an empty stomach. By adding protein, fiber, or fat to a meal, the glycemic index is lowered. Also, the GI ranking does not take into account how much food is normally consumed.
What does all of this mean? Drum roll, please! The overall consensus is that using GI alone for dieting would not necessarily result in weight loss. Remember portion size matters too. No matter the type of carbohydrate or the GI of the food, the more you eat, the more calories you will consume. If you do choose to eat a food with a high GI, have a smaller portion. Overall, try to include more whole grains, nuts, legumes, fruits and non-starchy vegetables in your diet and decrease your consumption of low GI carbohydrates and sweets (candy, cookies, cakes and sweetened drinks).
Mayo Clinic. Glycemic index diet: what’s behind the claims. Available at: http://www.mayoclinic.com/health/glycemic-index-diet/MY00770. Accessed August 3, 2015.
American Diabetes Association®. Glycemic index and diabetes. Available at: http://www.diabetes.org/food-and-fitness/food/planning-meals/glycemic-index-and-diabetes.html. Accessed August 3, 2015.