The glycaemic index is a measure of the speed at which a carbohydrate food is digested to its component glucose molecules and the rate at which this glucose is subsequently transported into the blood. This measurement is given a rating through comparison with powdered glucose or white bread. Foods with a higher glycaemic index are more rapidly digested and absorbed and therefore cause a sharper more pronounced rise in blood sugar levels.
Blood Sugar and Insulin
Glucose is absorbed to the blood where it circulates before entering cells to supply them with energy. In order for this to happen the hormone insulin is required. Insulin acts as a key that opens transporters in the cell membranes and this facilitates the entry of glucose. The more glucose that is absorbed to the blood, the more insulin that is required for its transport into cells. Foods high on the glycaemic index therefore cause excessive insulin release.
The Glycaemic Index and Insulin resistance
Regular consumption of high glycaemic index carbohydrates is associated with an increased risk of metabolic dysfunction. This is because rapid influx of glucose to the blood increases the uptake of glucose to the liver and this can result in the synthesis of fats. These fats are thought to accumulate in tissues and interfere with the action of insulin in its cell transport role. In this way high glycaemic index carbohydrates cause a disorder called insulin resistance.
The Glycaemic Index and Abdominal Obesity
Regular consumption of high glycaemic index carbohydrates therefore results in insulin resistance. Insulin resistance causes the cells of the liver and skeletal muscles to become unresponsive to the action of insulin. Instead of being shuttled into cells to be burnt as energy during exercise and for metabolic regulation, the glucose gets pushed into fat cells. This causes weight gain in the abdominal area, a disorder termed abdominal obesity.
The Glycaemic Index and Cardiovascular Disease
The metabolic dysfunction associated with insulin resistance and abdominal obesity increases the risk of cardiovascular disease. This is because the accumulation of fat in the abdomen causes the release of inflammatory cytokines and this increases systemic inflammation. This inflammation increases oxidative stress in the arteries of the body and this causes endothelial dysfunction. Endothelial dysfunction disrupts blood flow and raises blood pressure.
The Glycaemic Index and Cancer
High glycaemic index carbohydrates cause the release of excessive amounts of insulin. This is problematic because insulin also causes the release of insulin-like growth factors. These proteins increase the proliferation of cells and evidence suggests that high circulating levels of insulin-like growth factors can increase the proliferation of cancer cells. This explains the increased risk of cancer with regular consumption of high glycaemic index carbohydrates.