Glycemic index ([ Glycaemic Index, Glycemic Index, GI ] A numerical value associated assigned to specific foods that indicates its effect on blood sugar, measured two hours after consumption. The glycaemic index is relative to the consumption of pure glucose which is... More) has seen wide popularity among weight-loss dieters. Originally intended to be used by diabetics, it is a method of rating foods according to how much they impact a rise in blood [ Glucose, D-glucose, Dextrose ] A monosaccharide with the molecular formula C6H12O6. The principle isomer of glucose is D-glucose (dextrose). It is the product of photosynthesis and the building block of a number of important carbohydrate polymers, including cellulose. In... More levels.
Prior to the GI all that existed was the “Exchange System”, or “Exchange Lists” system of classifying foods. Developed in the 1950s, its purpose was to raise awareness about the [ Nutrient ] A substance that provides nourishment essential to life. Nutrients may either be organic, as in carbohydrates, fats, proteins and vitamins, or inorganic, as in minerals, oxygen and water. They are derived from the environment, typically food, and... More equivalency of foods in terms of [ Macronutrient ] A nutrient that is consumed in large quantities and forms the bulk of the biomass of an organism. In animals, the macronutrients are carbohydrates, fats and proteins. In plants, the macronutrients include calcium, magnesium, nitrogen, phosphorus, potassium... More, and classify them in such a way that food substitutions could be made that would provide nutritional equivalency. The Exchange System did not take into account that some foods impacted blood [ Sugar ] Any of the class of crystalline, water-soluble, short-chained (monosaccharide and disaccharide) carbohydrates. Sugars are typically sweet-tasting and include glucose, galactose, fructose, sucrose, lactose and maltose.... More more than others, regardless of their net [ Carbohydrate, Carb, Saccharide ] A group of organic compounds occurring in living tissues, comprising of sugars, starches, and cellulose. Carbohydrates can be divided into four chemical groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Shorter-chain carbohydrates (monosaccharides and disaccharides) are generally... More levels. The Glycemic Index did take this impact into account.
GI was the outcome of research done by Dr. David Jenkins and his team at University of Toronto. Jenkins, an MD and professor in the department of Nutritional Sciences at U of T, first wrote a paper on GI, published in the American Journal of Clinical Nutrition in 1981.
Jenkins’ team tested the most popular carbohydrate-based foods to determine the rate at which they raise blood glucose within a two-hour period after consumption. Pure glucose was given a reference GI value of 100. The higher the index number, the more rapidly the carbohydrate breaks down in the digestive tract and the more rapidly it raises blood sugar levels. Foods that contain zero [ Carbohydrate, Carb, Saccharide ] A group of organic compounds occurring in living tissues, comprising of sugars, starches, and cellulose. Carbohydrates can be divided into four chemical groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Shorter-chain carbohydrates (monosaccharides and disaccharides) are generally... More, such as animal protein and [ Fat ] • A subclass of lipids that includes fatty acids and triglycerides • Any of the fatty acids and fatty acid esters of glycerol which are solid at room temperature, compared to oil, which is a liquid at... More, were therefore considered as having a GI of zero.
The popularity of GI among weight watchers is related to the notion that simple carbohydrates can have more of an impact on weight gain that complex carbs.
A major criticism of GI is that it doesn’t take into the quantity consumed. Eating 10 bananas is definitely going to have more impact on your blood sugar than eating one, but GI still doesn’t tell us how many bananas we could or should actually consume.
So shouldn’t we abandon Glycemic Index altogether? Well, yes and know. I’ll talk about Glycemic load in my next instalment, you’ll see why we still need GI.