If you watch your blood glucose regularly you have probably noticed that some foods seem to raise your glucose high and faster that other foods. Even when you eat the same amount of carbohydrate, the effect can be strikingly different.
What is the Glycemic Index?
The Glycemic Index helps you to see the effect on your blood sugar after eating different foods. Many people maintain that all carbohydrates have essentially the same effect. And to some extent, that is correct. The difference is how the effect is produced over time. In order to understand the significance of the Glycemic Index you need to know a little about how food is absorded from the intestines.
Carbohydrates are broken down into sugars during the digestive process. The liver receives all the absorbed sugars through the portal vein. The liver stores these as glycogen, and later uses the glycogen to replensish the blood glucose level. When the rate of absorption exceeds 1 KCal/min the liver can no longer capture the sugar and it passes to the circulating blood. This raises the blood glucose level. The excess glucose is transported to fat cells for storage, however the fat cells can not release the stored sugar to replenish the blood glucose level like the liver can. The net result of this is that the fat stores increase, the blood glucose levels increase, and damage to the blood vessels, eyes, and kidneys may occur.
The Glycemic Index is a way to identify which foods raise the blood sugar quickly and which foods raise the blood sugar more slowly. The graph below illustrates the effect of food with a high Glycemic Index compared to food with a low Glycemic Index. Use the links on the left to find more information about the Glycemic Index, including lists of foods and software to help you select food that raises the blood sugar more slowly.
Glycemic index of different products
While there are about 500 foods that have had the Glycemic Index measured, the use of absolute numbers has been problematic. There are two main reasons for this.
- We seldom eat a single food, prepared in a single way. Usually we eat a “meal” of several different foods which vary in their index and carbohydrate content. There is no simple formula that will allow us to calculate exactly how much a particular meal will raise our blood sugar.
- We usually eat foods that have been calculated along with foods that have not been calculated. Again making it difficult to perform a precise calculation.
This does not in any way invalidate the index or mean that we should not consider it when planning our meals. Rather, it simply means that we need to pay particulat attention to the foods we eat. Most of us tend to eat a diet selected from a group of favorite foods. By comparing these with the tables of known indexes, we can estimate the relative impact of these foods. Keep a careful diary for a while including a carbohydrate count, estimated Glycemic Index, and blood glucose levels 2 hours after eating. Also measure a blood glucose level at 4 hours after eating.
Soon you will see a pattern to the foods and food mixes you commonly eat. You can then adjust the amount of these highly glycemic foods that you eat in one meal so that you will still meet your post-prandial (2 hours after eating) goals.
A journal is absolutely essential in order to seel these relationships. Use the glycemic indexes as a guideline to adjust your diet and use your own specific data to validate which of your foods have the most glycemic effects on you. Remember, the goal is to have your 2 hour post-prandial blood sugar less than 140 mg/dl and your hemaglobin A1c measurment less than 6.5.