GI is an abbreviation of the term "glycemic index" and is an indicator of how much your blood glucose level rises after a meal. In other words, it indicates how much of the sugar contained in foods are absorbed and is a measure of how much of that sugar is in your bloodstream up to two hours after you eat.
GI first began to attract attention in the 1990s and was the subject of a FAO/WHO report in 1998. In 2003, the WHO issued a report stating that low GI foods had the potential to reduce the risk of being overweight, obesity, and type 2 diabetes. Following that, a variety of studies were carried out, resulting in an increased demand for low GI foods, which contain high fiber and have a low energy density.
Low GI foods have drawn a lot of attention because they are associated with the improvement and prevention of obesity and metabolic syndrome, two conditions that more and more people suffer from nowadays.
The University of Sydney has defined foods with a GI value of over 70 as "high GI foods," foods with a GI value of between 55 and 70 as "mid-range GI foods," and foods with a GI value of 55 or under as "low GI foods."
So, what is the actual difference between low and high GI foods?
When you eat rice, bread, or any other typical food high in carbohydrates, it is digested by the stomach and small intestine, where it is absorbed into the blood as glucose. Figure 1 below shows how it is absorbed into the body
As shown in this diagram, the sugar in food is absorbed into the blood as glucose (1). The pancreas secretes insulin in reaction to the increase in glucose (2). Because the glucose is absorbed into the liver, muscle, adipose (fat) tissue and other cells (3), the blood sugar level drops to the level it was before anything was eaten. This is the mechanism found in healthy people.
When glucose enters the bloodstream, insulin facilitates its uptake into the body's cells. When an excess of glucose is ingested, insulin over secretion occurs. Insulin increases the biosynthesis of fat and suppresses its breakdown. Thus, it becomes easier for fat to accumulate in body tissues.
Blood sugar level will not drop if the sugar in the blood is not properly processed due to, for example, too little insulin being secreted, or resistance to the action of insulin. If blood sugar levels have not decreased several hours after eating on a regular basis, this indicates a susceptibility to diabetes. To avoid this and stay healthy, we should eat types of foods that will not cause a sudden, extreme rise in blood sugar levels.
This is where GI comes into the picture. Because high GI foods cause a sudden spike in the blood sugar level, large amounts of insulin are secreted in order to process the sugar in the blood, causing a spike in insulin secretion to handle the sugar. When low GI foods are eaten, the sugar is gradually absorbed into the body so the blood sugar level rises gradually. Thus, an appropriate amount of insulin is secreted and sugar is promptly taken up by the tissues.