The glycaemic index is a measure of the rise in plasma glucose following consumption of a carbohydrate food, with white bread or glucose as the reference food given a value of 100. Each carbohydrate food can be given a value that corresponds to its glycaemic effect and ranked against the reference food. This provides a useful to allow researchers to investigate associations with particular disorders. Generally, research to date has identified consumption of high glycaemic diets to be associated with obesity, metabolic syndrome and diabetes. In fact, dietary treatment of these conditions is centred around replacing high glycaemic foods with lower glycaemic alternatives. Further, the addition of fibre and protein to a diet lowers the glycaemic index of foods considerably, because both slow digestion of carbohydrate and decrease the rate of absorption to the plasma. This may explain the weight loss effects of both protein and fibre.
Because high glycaemic index diets are more likely to contain refined carbohydrates, they could be considered to be of poorer nutritional quality compared to diets containing lower glycaemic index foods. During the refining process, the bran and germ are removed to leave the starchy endosperm, and in this process most of the dietary fibre and micronutrients are removed. Refined carbohydrates therefore possess not only a higher glycaemic index due to the removal of fibre, but also are devoid of meaningful levels of micronutrients. Western nations have increasingly had their food supplied adulterated by high glycaemic refined carbohydrates, and evidence suggests that this is partially responsible for the increase in the prevalence of lifestyle diseases such as obesity and cardiovascular disease seen in these countries. That cardiovascular disease and obesity are associated with blood sugar disorders such as diabetes, metabolic syndrome and hyperglycaemia supports this contention.
Because of the possibly contribution of high glycaemic index diets to poor health, researchers1 have investigated the association between dietary glycaemic index and the risk of nutrient inadequacies in children. Data from a national dietary survey was analysed to assess the glycaemic index of diets of children aged between 2 and 16 years. In addition, the researchers calculated the odds ratio of the subjects for not meeting the nutrient reference values, lain down by the Australian state. Following logistical regression analysis, the results showed that children with higher glycaemic index diets were more likely not to achieve the recommended intake of nutrients for most nutrients. Subjects with a higher glycaemic index diet had a high risk of not obtaining the minimum recommended intakes of dietary fibre, calcium, potassium, phosphorus, magnesium, iodine, riboflavin, folate, vitamin A, vitamin D and vitamin E.
These results show that high glycaemic index diets are associated with poor nutrient intakes, and therefore such diets could be classified as of poor quality. These results are interesting because they may highlight the importance of low glycaemic index diets from a new perspective. It has been assumed that low glycaemic index diets are associated with obesity and cardiovascular disease because they cause poor glycaemic control. However, the low glycaemic index diets may produce micronutrient insufficiencies and this in turn may leads to metabolic abnormality and insulin insensitivity. For example, chromium is needed for the correct function of the insulin receptor. Eating a nutrient poor high glycaemic index diet may produce a chromium insufficiency which leads to insulin resistance. Chromium was not tested in this study, but other research has found high proportions of western populations to be deficient in chromium.
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