Since all calories are not created equal (290 calorie bison burger ≠ 290 calorie doughnut), what does it make sense to focus on as you shape up your diet? If we consider it essential to know your total protein, fat, and carbohydrate intake goals, then honing in on the glycemic profile of the carbohydrates you eat is a strong second. Carbohydrates, whether in bean sprouts or an Almond Joy, are converted to simpler sugars to fuel the body. Some carb sources, like Pixie Stix, fruit juice, or sugar in your coffee, which contain dextrose, fructose, and sucrose, require little or no digestion – they appear in the bloodstream quickly and are ready to use as fuel virtually immediately. Complex carbohydrates like those in whole grain bread, hummus, and black beans are converted more slowly.
This concept of “fast” and “slow” carbs is formalized by the glycemic index (GI) and glycemic load (GL). In a controlled research setting the index compares the blood sugar profile of healthy study participants consuming 50 grams of the carbohydrate being indexed to the blood sugar response of an equal amount of glucose over two hours after consumption. Glucose, the reference standard for the fastest carb has a GI value of 100. So a food that raises blood sugar half as much over the two hours has a GI of 50.
Lower and longer blood sugar response for the same number of grams of carbohydrate means lower insulin levels, less tendency to store excess as fat, and better control of hunger signals. Relatively few foods, just hundreds of the thousands of common foods we eat, have been formally tested for GI using the gold-standard method of “in vivo” testing in humans. At the high end of GI are baked potatoes at 80s to 90s and fruit roll ups, with a GI of 99. (Yes, we’ve been feeding our toddlers nearly pure sugar. In contrast, honey averages 55.) White wheat flour bread comes in at 70; cranberry juice cocktail at 68, oatmeal, 58. White rice is 68 compared to brown rice at 55.
At the low end are apples and milk (most in high 20s to 30s for GI) , barley and cashews at 22, soybeans at 18. For convenience sake, and to allow for estimation rather than direct testing, foods are more often grouped into high GI (from estimated GI of 70 and above) medium (from 69 to 55) and low (55 or lower). The concept of glycemic load (GL) further refines the GI by taking into account typical portion size. For foods that are bulky and high in fiber we may not consume as much as is required to consume the same volume of food as the 50 gram test dose required for GI comparison.
Tables grouping foods by GI are available in pocket book form and in reference tables online to help classify your favorite foods and special indulgences. Some resources are listed below. As a simple rule of thumb look at the nutrition label and pick foods with lower “sugar” grams as a proportion of the overall carbohydrate grams in the food.
K. Hartmann, MD, PhD
Resources:
Kay Foster-Powell, Susanna HA Holt and Janette C Brand-Miller. International table of glycemic index and glycemic load values : 2002, in American Journal of Clinical Nutrition, Vol. 76, No. 1, 5-56, 2002.
The Official Website of the Glycemic Index and GI Database from the international leaders in GI testing in Sydney Australia.
Glycemic Index and Glycemic Load for 100+ Foods from the Harvard Health Letter.