The Glycemic Index: A Powerful Weight-Loss Aid
All carbohydrates are not created equal. The same amount of carbohydratefrom different foods can affect blood sugar and insulin levels very differently. This has been proven by glycemic index testing of thousands of carbohydrate-containing foods on human volunteers from many parts of the world.However, in the United States, information is sometimes controlled by a profit-oriented establishment, so we have been slow to accept the empirical proof that not all carbohydrates have the same effect on our bodies.
Because of this suppression of evidence, many conventional doctors believe untruthsabout carbohydrates and treat diabetics based on this misinformation. These doctors prescribe a standard diabetic exchange system diet for their diabetic patients, and conventional dieticians help the patients implement these diets. They define one exchange of a carbohydrate food as the amount of that food which contains approximately 15 grams of carbohydrate. For insulin-dependent diabetics, the number of carbohydrate exchanges in their diets is balanced with their insulin dosages. However, because the carbohydrate in an exchange of, for example, white rice has a greater and more rapid effect on blood sugar levels than the same amount of carbohydrate eaten in thick-rolled oats or stone ground whole wheat bread, the amount and timing of the patient’s need for insulin differs. It’s no wonder so many diabetics have difficulty maintaining stable blood sugar levels!
Another false assumption is that all complex carbohydrates such as starches are “good” and have a gradual impact on blood sugar levels, but simple carbohydrates such as sugars cause a higher blood sugar spike very rapidly. This also has been proven false by the reproducible testing of thousands of foods on human volunteers world-wide. Most types of rice have a faster and more pronounced effect on blood glucose levels than table sugar does.
These assumptions were first challenged in the 1980s by Dr. David Jenkins at the University of Toronto in Canada. He measured the effects of a large number of foods on blood sugar levels of human volunteers. This testing became standardized and led to the development of the glycemic index, a system of scoring foods according to the effect they have on blood sugar levels of real people.
GLYCEMIC INDEX TESTING AND SCORES
Glycemic index scores are based on the testing of pure glucose as a reference food. (However, some of the early testing used white bread as a reference food, which is obviously not as easy to standardize as pure glucose). For standard glycemic index testing, eight to ten volunteers are given a dose of 50 grams of pure glucose. Their blood is drawn and blood sugar levels are measured periodically over the next two hours. For each patient, these blood test results are plotted on a graph of blood sugar level versus time, and the area under the curve of the graph is calculated. The test is repeated on two or three occasions and the results are averaged. Then, at another time, the volunteers eat a portion of the test food which contains 50 grams of carbohydrate. For example, if bread is the test food, they will each eat about 3½ slices of bread. Their blood sugar levels are again tested over a two-hour period, plotted on a graph, and the area under the curve of the graph is calculated. This area is divided by that volunteer’s average result when glucose was tested and the result of the division is multiplied by 100. The number obtained is the approximate glycemic index score (GI score or GI value) for the test food. This number is averaged with the result obtained for the other volunteers to calculate the GI score for the food tested. These GI tests for various foods have been shown to be reproducible in testing done in many countries around the world. The values obtained are reproducibly the same for both healthy volunteers and diabetics; however, diabetics have their blood drawn for a 3 hour period after the test meal rather than for two hours.
|The GI score reflects what really happens to our blood sugar when we consume a certain food. The surprising thing is that some complex carbohydrates have higher glycemic index scores than pure sugar. The GI score of a food cannot be predicted from whether it contains simple or complex carbohydrates or from the scores of foods in the same food category. (For example, fruits have a wide range of GI scores; grains have a similar wide range).
High fiber foods slow the impact of carbohydrates on blood sugar levels.
In order to determine the glycemic index of a food, it must be tested using real people. (1) Based on these test results, foods are classified as being high GI if their score is 70 or higher, intermediate or medium if their score is 56 to 69, or low on the GI scale if their score is 55 or less.
Foods are tested in the form in which they are eaten and many factors, such as cooking time and other ingredients included in the recipe, affect how rapidly the food is digested and absorbed. Therefore, how quickly and how much the food affects blood sugar levels depends on factors such as how much fat and protein are present and whether the food is cooked moderately or overcooked. For example, chocolate and high-fat ice cream have lower GI scores than white bread does because the fat they contain slows down their digestion and the absorption of the sugar they contain.
Another factor that influences the glycemic index score of a food and determines the effect it has on our blood sugar and insulin levels is what foods that are eaten with it in a meal (especially how much fat and protein the other foods contain) because they affect how quickly the carbohydrate is digested and absorbed. The amount and kind of fiber a food or meal contains affects the glycemic index of the food by slowing down the rate of digestion and absorption of the sugar or starch in the food. The GI score is also dependent on the amount and type of processing the food has undergone.
The physical state of the starch in a food also greatly affects its GI value. If the particle size in the food is small, such as in finely milled flour, it is easy for digestive enzymes and water to penetrate the food, and it will be quickly digested. If the starch is cooked or prepared in a way that allows it to absorb a lot of water, it will be more “gelatinized” (basically wet and soluble all the way through) thus resulting in quick digestion. Pasta which is cooked briefly to be al dente (giving resistance to the bite) rather than being cooked to mushiness has a lower GI score than overcooked pasta.
Table sugar refined from sugar cane or beets (sucrose) has a GI score of 60 which is in the medium range. This surprises us because sugar is supposed to be THE “bad” food! It has a medium score because each sucrose molecule is composed of two simple sugars, glucose and fructose. Digestion breaks the two molecules apart and the glucose molecule from each sucrose molecule (half of the carbohydrate) is absorbed rapidly. However, the fructose molecule (the other half of the carbohydrate) must go to the liver and be converted into glucose before it can enter the general circulation and impact blood sugar levels. This delay makes the GI score of table sugar considerably lower than that of pure glucose at 100.
HOW THE GLYCEMIC INDEX HELPS US
The glycemic index scores of carbohydrate foods help us make food choices which lead to more stable blood sugar and insulin levels. Choose most of your carbohydrate-dense foods from those which have low and moderate GI scores and balance them with protein to control the impact of your meals and snacks on your blood sugar and insulin levels.
In addition to the glycemic index score of a meal or food, the quantity eaten also determines the impact the meal or food has on blood sugar and insulin levels. How much carbohydrate is eaten is critically important. If you eat two cups of cooked pasta, it will have about twice the effect of eating one cup of pasta. The glycemic load of a meal or snack is a measure of the impact of that meal or snack that accounts for both the GI score and the amount eaten. To calculate GL (glycemic load), the GI of a food is multiplied by the number of grams of carbohydrate in the serving and that number is divided by 100.
The concepts of glycemic load and the glycemic index of foods can be used to develop an eating plan that does not over-stimulate the pancreas to produce a spike of insulin after any meal or snack. This keeps insulin levels stable and low throughout the course of the day which promotes the burning of stored fat rather than the formation and storage of new fat from foods recently eaten. Instead, recently eaten food is used for the immediate energy needs of daily activities. Thus, if your insulin is low and stable, you should be using both fat stores and your last meal to produce energy and may notice that you have more energy and are less hungry that you were before you began an eating plan based on glycemic control.
1. Testing is not needed for combination dishes or meals, such as a turkey sandwich; the GI can be calculated from the GI scores of the component ingredients and the amount of each used.