The glycaemic index is an often used measure of the degree to which a carbohydrate containing food can cause an elevation in blood glucose levels. The measurement is done with reference to 100 grams of carbohydrate from white bread or glucose, which are given a value of 100. Those foods with a higher glycaemic index cause a greater rise in blood glucose following consumption, per 100 grams of carbohydrate. However, the glycaemic index does not take into account the amount of carbohydrate consumed in a real world situation, something that can modulate the ultimate blood glucose levels, and for this reason the glycaemic load is a preferable tool. The glycaemic load is the the rise in blood glucose levels taking into account the amount of carbohydrate ingested in a partition of food. The glycaemic index and glycaemic load are important parameters to consider, because evidence increasingly shows that foods that produce large rises in blood sugar may have deleterious health effects.
However, the rise in blood glucose must always be taken in content. Parsnips for example have a very high glycaemic index, and if 100 grams of carbohydrates from parsnips is ingested, blood glucose levels will rise almost as quickly and to the same degree as when consuming pure glucose. However, parsnips have a much lower glycaemic load, because in reality, eating 100 grams of carbohydrate from parsnips would require the consumption of a very large portion. Consuming a small number of parsnips, something that would be realistic, produces a much smaller rise in blood sugar levels due to the very low total amount of carbohydrate in the food. This factor explains why certain foods can have very high glycaemic indices, but yet be classed as healthy food. A number of studies have investigated the association between the glycaemic load of diets as a whole and the weight loss experienced by those following such diets. Evidence suggests that a low glycaemic load diet may increase weight loss.
For example, in one study1, researchers investigated the relationship between changes to the glycaemic load of a group of individuals over 4 years, and the weight change experienced in the same period. In particular, the researchers were interested in how the addition of protein foods, known to lower the glycaemic index of a meal, would affect these changes. The results showed that addition of protein foods such as yoghurt, peanut butter, nuts, chicken, low-fat cheese, and seafood increased the weight loss seen in the subjects over the 4 year period. However, this effect was not evident for some other protein foods such as milk, legumes, peanuts, eggs or chicken with skin. However, as the protein content of the diet increased, there was a reduction in the glycaemic load of the diet suggesting that the weight loss effects from protein, may be due to the more favourable glycaemic control seen from such diets. Using protein foods to modulate the glycaemic load favourably, may therefore be an effective weight loss strategy.
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