Glycemic Index (GI) is a relative index system that measures the effect of different carbohydrates upon the density of glucose (sugar in the blood. The higher the index is, the faster the rise of density of glucose in the blood, even though the same amount of carbohydrate is taken. To calculate GI, the first step is to have the subject take a certain amount of a type of food which contains carbohydrates, normally 50g. The X-axis plots the time and the Y-axis plots the density of blood sugar. Take the Area Under the 2 hour blood glucose response Curve, AUC within two hours, divide by the reference AUC integration obtained from the test of white bread or glucose, and then multiply by 100 to get the GI of this food type. If we take the GI which has a glucose reference standard of 100, then the maximum GI we can get from the test will be 100 and that of GI of glucose will be 140, assuming that the GI of white bread is 100. Countries where breads are the main source of carbohydrates, should have the bread GI as the reference standard.
GI is used to measure the carbohydrate content in 5 grams of different types of food. The GI is not calculated for foods that contain little or even no carbohydrate. These include fish, meat, egg and most types of stalk vegetables (excluding root vegetables like potatoes and yams which contain great amount of carbohydrate but including Chinese radish) and liquors (strong liquor, wine and beer; the carbohydrate in liquor has been fermented into alcohol and alcohol calories is 7 per gram) Normally, a high GI can be found in food types that are easily and quickly digested by the human body. The simpler the molecular structure of the carbohydrate is, for example, sucrose, fructose, or liquids and drinks, the quicker it is digested. Furthermore, they are easily absorbed by the human body and released to the blood system as glucose. In contrast, vegetables and whole grains that contain a great amount of fiber and long-chain carbohydrates are not easily digested, decomposed and absorbed. Consequently, they have a low GI. Low GI foods have a lower need compared to high GI types.
Foods that have a GI of or below 65 are considered as low-insulin types. Low GI foods contain less carbohydrate. For instance, there is a greater amount of carbohydrate in bananas compared to strawberries; thus, the GI of bananas is higher. Another example is granulated sugar and fructose. Both belong to the category of carbohydrate; however, the former is a kind of two-molecule glucose and it has a GI value three times that of the latter. Having a low GI, fructose is not easily digested.
Cooking also affects the GI index. Cooked rice is not easily digested and it has a lower GI than rice porridge. Rice that has been dried out has an even lower GI. The GI of a food type can vary depending on the way it is cooked or processed. Low GI foods also contain a greater amount of fiber. Normally, vegetables have a low GI, for they contain lots fiber. Vegetables such as potatoes and sweet potatoes are excluded in this category, for they contain a great amount of carbohydrate.4. Low GI foods contain more fat and protein. GI has nothing to do with fat and protein and thus milk and cheese are low GI foods. Though they have a large amount of protein and fat, they have less carbohydrate.
GI means the effect of every gram of carbohydrate on the density of blood sugar in the human body. The quantity of carbohydrate is crucial to the density of glucose. The more carbohydrates we take, the faster the density rises. Consequently, another index, the Glycemic Load (GL), has been developed to measure the influence of food on blood sugar. To measure GL, we obtain the weight of carbohydrate (in grams) in a certain portion of food and multiply this weight by its GI and then divide it by 100. For instance, there are 42 grams of carbohydrate in a dish of 150 grams of cooked rice. Its GI is 45 and thus its GL is calculated as (42 x 45) / 100 = 18.9. This means that 150 grams of cooked rice has a weight of 18.9 grams of pure glucose. By calculating the GL of our daily meals, we get the amount of food that can be transformed into pure glucose. GL makes us understand that the density of our blood sugar depends on the amount of food we eat, even though we take low GI food. Low GI foods do not guarantee a low blood sugar density.
Low GI foods quench and delay the sensation of hunger. High GI foods increase the speed of secretion of insulin, decompose and dramatically decrease blood sugar. When insulin density decreases, Glucagons increase accompanied by the secretion of the hormones Epinephrine, norepinephrine and cortisone that all together make us feel hungry. This is why high GI foods make people feel hungry,eat more, and get fat.
High GI foods speed up the secretion of insulin and this could cause resistance to insulin. It could also cause the liver to produce triglyceride from the blood sugar, after the glycogen has reached its maximum amount. The lipocyte will be stored as fat increasing the triglycerides. Some time after taking meals, the blood sugar decreases very quickly. At this time, the secretion of glucagons increases, causing the triglycerides to transform to fatty acids, increasing triglyceride density. These lead to potential problems of cardio-vascular diseases. Some diets focus on taking low GI foods. High GI foods bring more fat to our bodies. However, some studies have shown a different conclusion. People who take high GI foods lose nearly the same weight as those who take low GI foods, if they take in almost equal food calories. Therefore, it is the total amount of calories of the food we take that is crucial to our weight change. If the calories are too high, we get fat, regardless of the amount of carbohydrates, fat or protein contained. Consider the condition of low blood sugar known as Hypoglycemia, which could be caused by taking high GI foods. This condition will make us feel tired and hungry for more high GI foods, leading to weight increase.