The Glycaemic Index (GI) is a rating of foods according to their actual effect on blood glucose levels. It is not a test carried out in a chemical laboratory.
To determine the glycemic index of foods, the foods are eaten by individuals, and their blood glucose levels tested after eating, to assess the effect of the food on blood glucose levels. In other words the glycemic index gives us an indication of how different foods affect the body’s “petrol” levels.
One could say that the GI of a food represents its blood glucose raising ability.
In the past, it was assumed that complex carbohydrates or starches, such as potatoes, mealiemeal (cornmeal) and bread, were digested and absorbed slowly, resulting in only a slight rise in blood glucose levels. Simple sugars, on the other hand, were believed to be digested and absorbed quickly, producing a large and rapid rise in blood glucose levles. Today, we know that these assumptions were incorrect, and that the general public, as well as diabetics, no longer need to avoid sugar altogether, provided it is used correctly. In fact, table sugar has a slightly more favourable effect on blood glucose levels than for example, potatoes, SA standard bread or rice cakes.
As early as the 1930’s scientists challenged the traditionally held view that the metabolic effects of carbohydrates can be predicted by classifying them as either “simple” or “complex”. In the 1970’s, researchers such as Otto and Crapo, examined the glycemic impact of a range of foods containing carbohydrates. To standardise the interpretation of glycemic response data, Jenkins and colleagues of the University of Toronto, Canada, proposed the Glycaemic Index (GI) in 1981.
This work disproved the assumption that equivalent amounts of carbohydrate from different foods cause similar glycemic responses ( the same rise in blood glucose levels). Furthermore, the researchers concluded that the carbohydrate exchange lists that have regulated the diets of most diabetics, do not reflect the physiological effect of foods, and are therefore no longer sufficient in controlling blood glucose levels! Both the amount of carbohydrate, and its rate of digestion and absorption (the glycemic index) determines the physiological response of the body.
Research done all over the world since then, confirms that the new way of ranking foods according to their actual effect on blood glucose levels is scientifically more correct. Consequently the Glycaemic Index (GI) was developed, whereby foods are ranked on a scale from 0 – 100, according to their actual effect on blood glucose levels. In South Africa, glucose is taken as the reference food and allocated a GI value of 100, since it causes the greatest and most rapid rise in blood glucose levels. All other carbohydrate foods are rated in comparison to glucose. Since the GI is a ranking of foods based on their actual effect on blood glucose levels, instead of on assumptions, it is much more accurate to use in the regulation of blood glucose levels.
The graph below shows the effect of high GI food on blood glucose levels. Blood glucose rapidly rises to a high peak (blood glucose surge) and then plummet down as quickly, causing a graph that looks much like a witches hat. Irritability, lack of concentration and aggression are a few of the consequences of rapidly falling blood glucose levels.
Using the glycemic index (GI) concept, those suffering from diabetes or low blood sugar (hypoglycaemia), slimmers, children with Attention Deficit Disorder and sportsmen, can all optimize their blood glucose control.
The graph above shows how low GI foods are digested and absorbed steadily over a period of 3 hours and keep blood glucose levels steady for this time.
By using the GI concept in combination with low fat eating, both triglycerides and blood pressure can be lowered and HDL-cholesterol (the “good” cholesterol) can be increased. For those wanting to lose weight, the increased satiety given by the lower GI foods, and the fact that less insulin (a hormone that also encourages the body to store fat) is secreted by a low GI diet, results in better fat loss. Even people suffering from cancer, gout and irritable bowel syndrome can benefit from low fat eating and the GI concept.
Remember, foods with a low GI, release glucose slowly and steadily into the bloodstream and do not over stimulate insulin secretion.
High insulin levels are implicated in all the diseases of our modern lifestyle such as high blood pressure, high cholesterol, high triglycerides, diabetes, hypoglycaemia, ADHD, obesity and coronary heart disease (CHD).