The metabolic syndrome is a cluster of metabolic disorders that centre around the development of insulin resistance. Many Western lifestyle disease including obesity, cardiovascular disease and type 2 diabetes are now associated with insulin resistance and metabolic syndrome. The carbohydrate food choices made by an individual are thought to play a significant role in the development of insulin resistance, and therefore the subsequent risk of developing a Western lifestyle disease. Generally, low glycaemic index carbohydrates are considered protective of insulin resistance whilst high glycaemic index carbohydrates are considered to increase the risk. However, this line of reasoning is slightly disingenuous because many healthy forms of carbohydrate have high glycaemic indices, whereas many refined or processed foods, considered of low quality, have low glycaemic indices. That being said, the glycaemic response to a food or meal has been shown to play some significant role in the risk of developing insulin resistance.
Regularly consuming high glycaemic index foods may therefore lead to a deterioration in the insulin system. A number of studies have investigated these effects in clinical trials involving animals, as well as healthy subjects and those with disorders of glucose homeostasis. For example, one study1 investigated the effects of a high glycaemic index breakfast on the glucose homeostasis of subjects with type 2 diabetes. The subjects therefore had some significant degree of insulin resistance prior to beginning the study, and in this regard were likely highly sensitive to the effects of the carbohydrates. The results of the study showed that the subjects experienced less favourable plasma glucose, insulin and ghrelin responses when a high glycaemic low fibre breakfast was consumed, in comparison to a low glycaemic index high fibre one. Ghrelin is a hormone that stimulates hunger, and the higher ghrelin response to the high glycaemic index breakfast suggests that appetite would be significantly higher subsequently in the day.
Consuming low glycaemic index breakfasts with a high fibre content may be especially important for those with already disrupted glucose homeostasis. Most ready made breakfast cereal are by their nature of high glycaemic index and often contain added sugar that may be additively detrimental to glucose homeostasis. Avoiding such cereals should therefore be a priority for those with type 2 diabetes, or impaired insulin sensitivity. Oats have consistently been identified as improving insulin sensitivity and causing weight loss effects, and this may relate to their low glycaemic indices as well as their high content of soluble fibre. The ability of high glycaemic index diets to stimulate appetite through exaggerated ghrelin responses suggest that this may a significant contributory factor in overeating refined carbohydrates. This overeating leads to further blood sugar aberrations, and this cycle then causes a gradual deterioration of the insulin system, resulting in insulin resistance and weight gain.
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