The glycemic index is a ranking of carbohydrates based on their immediate effect on blood glucose (blood sugar) levels. It compares foods gram for gram of carbohydrate. Carbohydrates that breakdown quickly during digestion have the highest glycemic indexes. The blood glucose response is fast and high. Carbohydrates that break down slowly, releasing glucose gradually into the blood stream, have low glycemic indexes. The glycemic index (GI) is a ranking of carbohydrates on a scale from 0 to 100 according to the extent to which they raise blood sugar levels after eating. Foods with a high GI are those which are rapidly digested and absorbed and result in marked fluctuations in blood sugar levels. Low-GI foods, by virtue of their slow digestion and absorption, produce gradual rises in blood sugar and insulin levels, and have proven benefits for health. Low GI diets have been shown to improve both glucose and lipid levels in people with diabetes (type 1 and type 2). They have benefits for weight control because they help control appetite and delay hunger. Low GI diets also reduce insulin levels and insulin resistance. Recent studies from Harvard School of Public Health indicate that the risks of diseases such as type 2 diabetes and coronary heart disease are strongly related to the GI of the overall diet. In 1999, the World Health Organization (WHO) and Food and Agriculture Organization (FAO) recommended that people in industrialized countries base their diets on low-GI foods in order to prevent the most common diseases of affluence, such as coronary heart disease, diabetes and obesity.
About the Glycemic Index
The Glycemic Index (GI) relates to the way your body’s sugar levels respond to certain foods. Foods are given a rating from 0 –100 on the glycemic index with glucose in the highest position. High Glycemic Index foods (such as simple carbohydrates) will increase the body’s sugar levels rapidly whereas low glycemic index foods will increase the body’s sugar levels slowly. A good understanding of the glycemic index can assist in weight loss and help control diabetes. How Does the Glycemic Index work?
The glycemic index is complicated and cannot be generalized to all people. Different people will have different reactions to food. The body’s response to food will relate to several factors including; age, activity level, insulin levels, time of day, amount of fiber and fat in the food, how refined (processed) the food is, and what was eaten with the food. In addition to this, other factors such as the ratio of carbohydrates to fat and protein as well as how the food was cooked (e.g.. Boiled compared to fried or baked) and metabolism will determine the way your body’s sugar level responds after eating. Foods that have a low glycemic index will have little effect on the body’s sugar levels. Comparatively, foods that have a high glycemic index will have an instant affect on blood sugar levels. Ratings on the glycemic index have resulted from numerous studies; however, individuals should test their own reactions to food in relation to the glycemic index. The Glycemic Index and Food Foods low on the glycemic index will release glucose gradually into the blood stream whereas foods high on the glycemic index will provoke an immediate response in the blood sugar levels. Foods that contain carbohydrates are usually high on the glycemic index and have the greatest effect on blood sugars. Pasta dishes, bread and potatoes are usually high on the glycemic index. The composition in the carbohydrate will also affect how the body’s sugar levels react. For example, white bread will rate high on the glycemic index whereas wholegrain or rye bread will be rate lower on the glycemic index as it contains more grains and contains complex carbohydrates.
Examples of low glycemic foods are breakfast cereals (which are based on wheat bran, barley and oats), wholegrain break, fruit, lentils, soybeans, baked beans etc. Examples of high glycemic foods are white bread, soft drinks, full fat ice-cream, chocolate bars etc.
Health experts and dieticians contest that the glycemic index is difficult to use because it is complicated and will vary from person to person. They do concede however, that the glycemic index is a useful meal-planning tool especially when individuals monitor their own individual responses to foods. Low glycemic food is especially helpful in assisting those who want to lose weight. Low glycemic index foods will increase the sugar levels in the body to sustain energy levels for longer periods of time. This means an individual will feel less inclined to eat because energy is being slowly released into their bloodstream.
A good understanding of the glycemic index will also assist with exercise. If you exercise then eating high glycemic foods will help you recover from your workout. Specifically, faster carbohydrates that are high on the glycemic index are great for raising low blood sugars after intense exercising whereas low glycemic index foods are helpful in maintaining blood sugar levels for long periods of exercise. Health experts encourage using the glycemic index in conjunction with other meal programs to assist in managing diabetes and/or controlling weight. How Glycemic Load Improves the Glycemic Index Although most candy has a relatively high Glycemic Index, eating a single piece of candy will result in a relatively small glycemic response. Why? Well, simply because your body's glycemic response is dependent on both the type AND the amount of carbohydrate consumed. This concept, know as Glycemic Load, was first popularized in 1997 by Dr. Walter Willett and associates at the Harvard School of Public Health. Glycemic Load is calculated this way:
GL = GI/100 x Net Carbs (Net Carbs are equal to the Total Carbohydrates minus Dietary Fiber) Therefore, you can control your glycemic response by consuming only low-GI foods and/or by restricting your intake of carbohydrates. The Glycemic Index Yields Some Surprises Nutritionists used to believe that all simple sugars digested quickly and caused a rapid rise in blood sugar, and that the opposite was true for "complex carbohydrates". But that's not always the case. While many sweet and sugary foods do have high GI's, some starchy foods like potatoes or white bread score even higher than honey or table sugar (sucrose)!
Why is the Glycemic Index Important? Your body performs best when your blood sugar is kept relatively constant. If your blood sugar drops too low, you become lethargic and/or experience increased hunger. And if it goes too high, your brain signals your pancreas to secrete more insulin. Insulin brings your blood sugar back down, but primarily by converting the excess sugar to stored fat. Also, the greater the rate of increase in your blood sugar, the more chance that your body will release an excess amount of insulin, and drive your blood sugar back down too low. Therefore, when you eat foods that cause a large and rapid glycemic response, you may feel an initial elevation in energy and mood as your blood sugar rises, but this is followed by a cycle of increased fat storage, lethargy, and more hunger!
Although increased fat storage may sound bad enough, individuals with diabetes (diabetes mellitus, types 1 and 2) have an even worse problem. Their bodies inability to secrete or process insulin causes their blood sugar to rise too high, leading to a host of additional medical problems. The theory behind the Glycemic Index is simply to minimize insulin-related problems by identifying and avoiding foods that have the greatest effect on your blood sugar. Should All High-GI Foods be Avoided? For non-diabetics, there are times when a rapid increase in blood sugar (and the corresponding increase in insulin) may be desirable. For example, after strenuous physical activity, insulin also helps move glucose into muscle cells, where it aids tissue repair. Because of this, some coaches and physical trainers recommend high-GI foods (such as sports drinks) immediately after exercise to speed recovery.
Also, it's not Glycemic Index alone that leads to the increase in blood sugar. Equally important is the amount of the food that you consume. The concept of Glycemic Index combined with total intake is referred to as "Glycemic Load", and is addressed in the next section...
Limitations of the Glycemic Index and the Glycemic Load Some proponents of the Glycemic Index (including many diet books authors) would like you to believe that GI and GL are all that matters when selecting which foods to eat. In reality, diet is a more complex issue than that. ND agrees that the Glycemic Index is a marvelous tool for ranking carbohydrates (and much better than the old "simple" and "complex carbohydrate" designations). However, there are also many limitations to GI and GL, which are explained in this section. Consider this the warning that those diet book authors don't want you to hear...
