Glycemic Index

What is it?

The glycemic index ranks foods on how they affect our blood sugar levels. This index measures how much your blood sugar increases in the two or three hours after eating.

The glycemic index is about foods high in carbohydrates as foods high in fat or protein don't cause your blood sugar level to rise much. A lot of people still think that it is plain table sugar that people with diabetes need to avoid. The experts say that the glycemic index shows that even complex carbohydrates like baked potatoes, can be even worse.

Glycemic index is a useful tool that measures how fast a particular food is likely to raise the blood sugar. It can be very helpful in managing blood sugar levels. For example, if your blood sugar is low or it is dropping during exercise, you would prefer to eat carbohydrates that raise your blood sugar quickly. On the other hand, if you want to keep your blood sugar from dropping during a few hours of mild activity, you might prefer to eat extra carbohydrate with a lower glycemic index and longer action time. And if your blood sugar tends to spike after breakfast, you would want to select a cold cereal with a lower glycemic index.

Recent Findings

Before the development of the glycemic index beginning in 1981, scientists assumed that our bodies absorbed and digested simple sugars quickly, producing rapid increases in our blood sugar level.

But now it is known that simple sugars don't make blood sugar rise any more rapidly than some complex carbohydrates do. Of course, simple sugars are simply empty calories, and still should be minimized for that reason. Many of the glycemic index results have been surprises. For example, baked potatoes have a glycemic index considerably higher than that of table sugar.

The GI is especially useful to people with diabetes who want to plan their diets to minimize the incidence of high blood sugar, or spikes. It measures how fast the carbohydrate of a particular food is converted to glucose and enters the bloodstream. The lower the number the slower is the action. The numbers are percentages with respect to a reference food, which are given with respect to glucose.

Using glycemic index to prepare healthy meals helps keep your blood sugar levels under control. Experts thought that our bodies absorbed starches such as rice and potatoes slowly, causing only small rises in blood glucose, which was proved to be false.

Recent studies of large numbers of people with diabetes show that those who keep their blood sugar under tight control should avoid the complications that this disease can lead to. Most experts agree that what works best for people with diabetes is regular exercise, little saturated or trans fat, and a high-fiber diet.

The recommendations to exercise and eat more fiber and less saturated and trans fats is excellent advice as far as it goes but the real problem is carbohydrates. The official consensus remains that a high-carbohydrate diet is best for people with diabetes. However, some of the experts recommend a low-carbohydrate diet, because carbohydrates can raise blood sugar to dangerous levels. But that’s not the case with all carbohydrates, as all these carbohydrates don’t act the same way. Some are quickly broken down in the intestine, causing the blood sugar level to rise rapidly.

However, a GI value tells only how rapidly a particular carbohydrate turns into sugar. It doesn't tell how much of that carbohydrate is in a serving of a particular food. Four extensions of the glycemic index concept address this limitation.

• One extension is called the glycemic load, which is the glycemic index of a food times its carbohydrate content in grams.
• Similarly the adjusted carbohydrate exchange was developed, which refines carbohydrate exchange lists by multiplying the glycemic index of a food by its carbohydrate content to indicate the likely effect of a food on blood glucose.
• The concept of relative glycemic potency compares equal weights of foods.
• The concept of substance glycemic index was developed based on a fixed weight of foods.

Determining Glycemic Index

The glycemic index is about the quality of the carbohydrates, not the quantity. Obviously, quantity matters too, but the measurement of the glycemic index of a food is not related to portion size. It remains the same whether you eat 10 grams of it or 1000 grams. You can eat twice as many carbohydrates in a food that has a glycemic index of 50 than one that has a glycemic index of 100 and have the same blood glucose response.

Basically, test foods are fed to various people, some with diabetes, others without, in portions that contain 50 grams of available carbohydrates. The 50 gram carbohydrate portion is specified as 50 grams of available carbohydrates, which means it excludes the fiber. Researchers always use a 50 gram available carbohydrate portion and often rely on manufacturers to give the composition data.

Important Diet Considerations:

Glycemic index should not be the only criterion when selecting what to eat. The total amount of carbohydrate, the amount and type of fat, and the fiber and salt content are also important dietary considerations. The glycemic index is most useful when deciding which high-carbohydrate foods to eat. But don't let the glycemic index persuade you into eating more carbohydrates than your body can handle, particularly if you have diabetes. The number of grams of carbohydrate consumed is awfully important. Make sure you know the carbohydrate content of the foods you eat.

The problem is that even among the complex carbohydrates not all are created equal. Some break down quickly during digestion and can raise blood glucose to dangerous levels. These are the foods that have higher glycemic indexes. Other carbohydrates break down more slowly, releasing glucose gradually into our blood streams and are said to have lower glycemic indexes.

But first you need to decide the composition of your diet in terms of carbohydrate, fat, and protein. Almost all the experts agree that we should minimize our intake of saturated and trans fat and eat a lot more fiber than we do. Some other fats, particularly those from cold-water fish and essential fatty acids such as found in large amounts in flax oil, seem to be beneficial. Beyond that, the battle rages between those who would have us eat more protein and those who say that carbohydrates should provide most of our calories. Generally, foods high in fat and protein have lower glycemic indexes than foods high in carbohydrate. In a real sense, the glycemic index is not applicable to high-fat and/or high-protein foods.

In addition, the glucose response to a particular food may be somewhat individual. So it is probably a good idea to carefully watch your own blood glucose level after eating foods you have questions about and determine if they have high or low GI for you.