The glycemic index (GI) is a measure of a food’s effect on the blood glucose level in the body.
A food with a low GI releases sugar into the bloodstream slowly, meaning the blood glucose level remains relatively constant. A food with a high GI causes a sharp “spike” in the blood glucose level. Maintaining a diet that consists of low GI foods over long periods of time has shown to be beneficial in the prevention of type 2 diabetes and coronary heart disease.
Recent evidence shows that daily consumption of high GI foods is a risk factor for the development of obesity. For example, a study comparing rats that were fed either high or low GI foods for 18 weeks showed that those on the high GI diet were 71% fatter and 8% less lean in body mass compared to the rats fed a low GI diet. The rats that were fed on a high GI diet also had significantly higher insulin and glucose levels after a meal as well as a blood triglyceride level that was three times higher than in the rats fed a low GI diet.
Frequent spikes in the blood glucose level are thought to promote diabetes and coronary heart disease by directly raising insulin levels, by increasing glycative stress and by increasing oxidative stress in the blood vessels.
Foods with a low glycemic index release sugar into the bloodstream slowly, therefore preventing sharp increases in glucose and therefore insulin. In the long term, this is thought to prevent insulin resistance, a condition where cells in the body no longer respond properly to the presence of insulin. Insulin resistance can eventually lead to type 2 diabetes.