GI Diet :: Glycemic Index of Foods
GI values can be interpreted intuitively as percentages on an absolute scale and are commonly interpreted as follows:
Low GI – less than 55
Intermediate GI – between 56 and 69
High GI – higher than 70
A low GI food will release energy slowly and steadily and is appropriate for diabetics, dieters and endurance athletes. A high GI food will provide a rapid rise in blood sugar levels and is suitable for post-endurance exercise energy recovery.
Previously, white bread was sometimes used as a reference food (if white bread = 100, then glucose = 140). For people whose staple carbohydrate source is white bread, this had the advantage of conveying directly whether replacement of the dietary staple with a different food would result in faster or slower blood glucose response. The disadvantages with this system were that the reference food was not well-defined, and the GI scale culture dependent.
The glycemic effect of foods depends on a number of factors such as the type of starch (amylose vs amylopectin), physical entrapment of the starch molecules within the food, fat content of the food and increased acidity of the meal – adding vinegar for example, will lower the GI. The presence of fat or dietary fibre can inhibit carbohydrate absorption, thus lowering the GI. Unrefined breads with higher amounts of fibre generally have a lower GI value than white breads but, while adding butter or oil will lower the GI of bread, the GI ranking does not change. That is, with or without additions, there is still a higher blood glucose curve after white bread than after a low GI bread such as pumpernickel.
The glycemic index applies to foods that contain carbohydrate only. High fat and high protein foods such as meat, eggs, nuts and cheese have a negligible GI. Furthermore, because many fruits and vegetables (but not potatoes) contain very little carbohydrate per serve, they have very low GI values and are regarded as “free” foods. This also applies to carrots which were originally and incorrectly reported as having a high GI (Brand-Miller et al, 2005). Alcoholic beverages are also low GI.