The glycemic index is a measure of how different carbohydrate foods affect your blood sugar levels. Food receives a score of zero to 100, depending on how quickly blood sugar rises after you eat it; the faster the rise, the higher the GI score. Generally, whole wheat carbs have lower GI scores than their white alternatives.
Hitting a Low Score
Whole wheat carbs usually rank lower than white carbs because they take longer to digest. Whole wheat grains haven't had the same refining process, so they're absorbed into the blood more slowly, according to dietitian Joy Bauer. This means it takes longer for your body to break them down; they cause less of a rise in blood sugar levels and therefore score lower on the glycemic index.
Not So Fast
To make it confusing, while you may generally think as whole wheat carbs as brown carbs, some whole wheat products actually are labeled as white. The difference is the type of wheat used, according to the Whole Grains Council. This often applies to bread, with white wheat used in white whole wheat and red wheat used in regular whole wheat. Check the label to ensure the first ingredient is stated as either "whole wheat" or "whole grain."
Whole wheat products tend to be much higher in fiber, because whole-wheat flour still contains the bran, germ and endosperm of the grain. These products and the fiber contained within them contribute to the slower digestion speed and lower glycemic index. According to the American Heart Association, whole wheat and whole grain products keep you feeling fuller longer and protect against high cholesterol and heart disease.
Problems with the Glycemic Index
While glycemic index seems like a valid method for measuring how healthy a food is, glycemic load may be better. Glycemic index doesn't take into account the amount of food consumed, whereas glycemic load is based on a standard serving size. The less refined a whole wheat product, the lower its glycemic index and load score will be. Whole wheat kernels, for instance, only score a GI of 30, but by turning this wheat into bread, you take the score up to 70, so look for products that are as unrefined as possible.