What is the Glycemic Index?
The glycemic index is a way of measuring the relative impact of foods on blood sugar levels. Foods with a high glycemic index have carbohydrates that the body can quickly convert to sugar, which makes them more likely to cause a quick rise in blood sugar. Many popular diets (Atkins and South Beach, for example) include food choices based on the glycemic index.
To determine the glycemic index of a food, human subjects are given a portion of a single food and their blood sugar is tested at intervals. The resulting response curve is compared to a control substance (either glucose or white bread) and assigned a numerical value. Glucose (or white bread) is given an arbitrary rating of 100, and all other foods are measured relative to that. Foods that rate above 100 are foods whose carbohydrates digest very quickly and are likely to raise the blood sugar immediately, while those with an index lower than 100 have less impact on the blood sugar.
What Makes a Food Low Glycemic?
Foods with few to no carbohydrates, like meats, cheeses and fats, will likely result in a glycemic index close to zero. The fewer easily-digested sugars and starches a food contains, the less likely it is to create a spike in blood sugar. Dietary fiber, while classified as a carbohydrate, passes through the system undigested, so it has no impact on blood sugar. In fact, fiber works to help slow the absorption of digestible carbohydrates.
Combining High and Low Glycemic Foods
The glycemic index of individual foods can be used as a guideline for meal preparation, but since most of us do not make an entire meal of one food, the interaction of foods in the stomach must also be taken into consideration.
Some foods act to reduce the overall glycemic level of a meal. Similar to the effect of dietary fiber, fats consumed with a higher glycemic food can also help to curb its blood-sugar-raising property. Likewise, vinegar has been found to inhibit the digestion of starches in the stomach. So, for instance, starting your dinner with a salad dressed in italian dressing (fiber + fat + vinegar) should lessen the impact of high glycemic foods in the meal.
What is Glycemic Load?
Like the glycemic index, the glycemic load of a food is used to characterize its potential effect on blood sugar. A food may have a high glycemic index, meaning the carbohydrate it contains will quickly convert to sugar, but if that food does not contain much carbohydrate per average serving, there will not be much impact on the blood sugar.
To calculate the glycemic load of a food, multiply its glycemic index by the number of digestible (non-fiber) carbohydrates in a single serving, then divide by 100. That number may be interpreted as follows:
- 20 and above = high glycemic load
- 10 to 19 = medium glycemic load
- less than 10 = low glycemic load
How Does Agave Nectar Compare?
|food||carbohydrates||x||glycemic index||÷||100||=||glycemic load|
|12 oz. regular cola:||40.5||x||90||÷||100||=||36.4|
|fresh apple (medium)||21||x||54||÷||100||=||11.3|
|2 Tbsp. agave nectar||32||x||30||÷||100||=||9.6|
Once can see that even though the apple has fewer carbohydrates, the glycemic load of the agave nectar is actually lower.