The glycaemic index (GI) is an important research tool that relates to the rise in the blood glucose levels following consumption of carbohydrate foods. The glycaemic index allocates a value of 100 to the blood glucose response to white bread or glucose. Particular carbohydrate foods are then compared to these foods and allocated a value. White bread and glucose are chosen as reference foods because of the high values they produce. High glycaemic index foods therefore result in faster rises in blood sugar and this increases the energy delivered to cells per unit time. High glycaemic index foods that give large rises in blood sugar are increasingly being linked to diseases of developed nations including obesity, cardiovascular disease and type 2 diabetes. However, while the glycaemic index is a useful research tool, it is perhaps not as useful as a real-world tool when compared to the glycaemic load (GL). This relates to the fact that the glycaemic load also takes account of the amount of carbohydrate consumed.
For example, a particular food may have a high glycaemic index. However, if only a very small amount of this food is consumed then the rate of blood glucose rise might be rapid, but the total rise in blood sugar will be small. Consuming high glycaemic index foods in small quantities therefore may not have detrimental health effects, because this limits the energy supplied to the cells, and it is the energetic overloading of the cells that is detrimental to cellular function, particularly by causing the development of insulin resistance. Parsnips for example have a high glycaemic index but they contain only limited amounts of carbohydrate. The rise is blood sugar is therefore rapid when consuming parsnips, but the energy delivered to the cells is still within the cellular capacity to cope. Parsnips are therefore not associated with disease, but in fact the phytonutrients and fibre may have beneficial effects. The glycaemic index is therefore not a good measure of disease causing capacity in the real world.
In contrast, the glycaemic load is a more useful measure of the disease causing capacity of carbohydrate foods. This is because the glycaemic load takes into account the total amount of carbohydrate consumed as well as the rate of glucose appearance in the blood. If therefore more accurately represents the energy supplied to the cells which is a better measure of disease. This explain the weight loss effects of consuming smaller amounts of food over a larger number of meals in the day, or a grazing pattern of consumption. Such a strategy reduces the energy supplied to the cells at each meal and allows the maintenance of insulin sensitivity, which has beneficial effects against weight gain. Exercise creates an environment of increased nutrient requirement and during this time high glycaemic index carbohydrates in larger amounts (i.e. a higher glycaemic load) can actually be beneficial. The timing and quantity of carbohydrates is therefore just as important as the glycaemic indices attributed to them.
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