Glycemic Index And Glycemic Load

The glycemic index and glycemic load measure how quickly the carbohydrate in a food is broken down by the body into glucose (blood sugar). Once a carbohydrate has been broken down into glucose, the hormone insulin moves the glucose from the blood into the cells of the body, where it's used for energy. Excess glucose is converted into glycogen and stored primarily in liver and muscle cells for future use.

Your body performs best when your blood sugar is kept relatively constant. If your blood sugar rises rapidly, it will then drop rapidly, leaving you feeling tired and prone to food cravings. High blood sugar has also been linked to weight gain, diabetes, heart disease, stroke, and some cancers.

The glycemic index (GI) is a scale from 0 to 100. The higher the number a food has, the more quickly it's broken down into glucose. Under 55 is considered to be a low GI value, above 70 is a high GI value, and in between is a medium GI value.

The glycemic load (GL) is a combination of the GI value of a food and the amount of food consumed. The amount of food consumed is just as important as the GI value of a food. For instance, most candy is relatively high on the GI, but eating a small piece of candy will result in a relatively small glycemic response. This is because your body's glycemic response is dependent on both the type of food consumed AND the amount of food consumed.

Glycemic Load = Glycemic Index/100 x Net Carbohydrate (Net Carbohydrate is equal to Total Carbohydrate minus Dietary Fiber).

In general, complex carbohydrates are broken down into glucose more slowly than simple carbohydrates, although this is not always the case. Potatoes and carrots are complex carbohydrates that are broken down into glucose very quickly because they are high on the GI. Apples are simple carbohydrates that are broken down into glucose very slowly because they are low on the GI.

Many popular diet programs base their food choices entirely on the glycemic index, stating that high GI foods are fattening and low GI foods are not. This is an oversimplification, as nutrition is more complicated than that. Also, the glycemic index, and consequently the glycemic load, have limitations:

• Wide variation in GI values. GI values are generally averages of several tests, and individual test results can vary quite a bit. For example, baked Russet potatoes have been tested with a GI as low as 56 and as high as 111. The GI value of certain fruits has been shown to increase as the fruit ripens. This amount of variation adds a great deal of uncertainty to GI values.

• GI values are affected by how a food is prepared. Generally, any significant food processing, such as grinding or cooking, will elevate GI values for certain foods, because it makes those food quicker and easier to digest. Even subtle differences in preparation, such as boiling pasta for 15 minutes instead of 10, affect GI values.

• GI values are affected when foods are combined. Tests for GI values are usually done on individual foods, but people often consume combinations of foods. The addition of other foods that contain fiber, protein, or fat will generally reduce the GI value of a meal.

• Individual differences in glycemic response. The rate at which different people digest carbohydrates varies, so there are some individual differences in glycemic response from person to person. It has also been shown that one person's glycemic response may vary from one time of day to another.

In conclusion, the glycemic index and glycemic load can be helpful in determining what foods to eat, but they should not be the only criteria used for determining what foods to eat.