The concept of glycemic index of foods was developed to compare the postprandial (after food) response on the blood glucose levels after eating a constant amount of different carbohydrate-containing foods. Simply put, to observe if there is any marked difference in the levels of blood glucose after eating refined foods like white bread and high fiber foods like fruits or vegetables.
The glycemic index is basically a measure of the change in blood glucose following intake of carbohydrate-containing foods. There are some foods (like sweets and chocolates) which result in a marked rise followed by a rapid fall in blood glucose, whereas others produce a smaller peak along with a more gradual decline in plasma glucose. This drastic blood sugar level fluctuation is not desirable as it may promote heart diseases by increasing oxidative stress to the vasculature, alter the insulin response and also lead to mood swings and hypoglycemic episodes. A low GI food will release glucose more slowly and steadily and is thus desirable.
The glycemic loads of foods, meals, and diets are calculated by multiplying the glycemic index of the constituent foods by the amounts of carbohydrate in each food and then totaling the values for all foods. Foods with low glycemic indexes include oats, barley, bulgur, beans, lentils, legumes, pasta, whole wheat, rye, wheat bread, apples, oranges, milk, yogurt, and ice cream. Fiber, fructose, lactose, and fat are the dietary constituents that tend to lower glycemic response.
If eating carbohydrates increase blood glucose, then shouldn’t we restrict the intake of carbohydrates in our diets?
Well, absolutely not. The dietary carbohydrate is an important component of a healthy diet. Carb digestion provides us with glucose, which is the primary fuel used by the brain and central nervous system. Moreover, the foods that contain carbohydrate are also important sources of many nutrients such as water-soluble vitamins and minerals as well as fiber. Even in diabetics, a low-carbohydrate diet is not recommended. Blood glucose is increased in individuals with diabetes in both the fed and fasted state. This abnormal metabolic response is due to insufficient insulin secretion, insulin resistance, or a combination of both. Although dietary carbohydrate increases postprandial glucose levels, avoiding carbohydrate entirely will not return blood glucose levels to the normal range. So it is imperative to have diets which provide 45–65% of calories from complex carbohydrate, with a minimum intake of 130 g carbohydrate/day for adults.
Knowing the glycemic index of a particular food helps in choosing the source of right carbohydrate in our diet and also which ones to avoid. The higher the rank of the carbohydrate ingested, the quicker it raises sugar levels in our blood, and hence more drastic fluctuations in the blood sugar levels and higher risk to related symptoms.
Glycemic Index Food Chart
Low Glycemic Index food (less than 55)
Foods with GI index between 55 and 70 are consider intermediate
High Glycemic Index food GI (more than 70_
A high GI food causes a more rapid rise in blood glucose levels and is suitable for energy recovery after endurance exercise or for a person experiencing low blood sugar levels.
In addition to the glycemic index, there are a variety of factors intrinsic to a given food that can influence its impact on blood glucose. These include the physical form of the food (i.e., juice versus whole fruit, mashed potato versus whole potato), ripeness, degree of processing, type of starch (i.e., amylose versus amylopectin), style of preparation (e.g., cooking method and time, amount of heat or moisture used), and the specific type (e.g., sphagetti versus macaroni) or variety (e.g., long grain versus white) of the food. Extrinsic variables such as the intake of protein and fat with carbohydrate sources, and degree of insulin resistance will also alter the effect of a specific carbohydrate-containing food on blood glucose concentration.