High glycaemic load diets associated with insulin resistance

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When carbohydrate is eaten, blood sugar (glucose) levels usually rise. The speed and extent to which blood sugar releases into the bloodstream has important implications for health. For example, the greater the level of blood sugar disruption, the more insulin will tend to be secreted by a functioning pancreas in response. High levels of this hormone predispose towards weight gain, as well as ‘insulin resistance’ ” a state where the body becomes somewhat ‘numb’ to the effects of insulin. In time, this may cause blood sugar levels to rise, which potentially can lead to the development of type 2 diabetes.

The speed and extent to which a food releases glucose into the bloodstream can be measured and expressed as its ‘glycaemic index’. The higher the glycaemic index, the more disruptive a food tends to be, and (all other things being equal), the worse it is for us. The thing is, though, other factors influence the effect a food will have on health, and one of the most important here is how much we eat of that food. For instance, it stands to reason that eating a lot of a high-GI food is doing to be generally more detrimental to the body than eating only a small amount of it.

This concept has spawned the development of another measure of the effect of food in the body known as the ‘glycaemic load’. The glycaemic load of a food is calculated by multiplying its GI by the amount of carbohydrate contained in a standard portion of food. This figure is then divided by 100. Basically, a food’s glycaemic load (GL) is thought to give a more realistic guide to the impact of that food on blood sugar and insulin balance.

High GL diets would be expected to lead to generally higher levels of insulin, which by rights should increase the risk of insulin resistance too. This idea got some support this week in the form of an article published on-line in the European Journal of Clinical Nutrition [1]. In this study, the relationship between dietary GL and risk of insulin resistance in women aged 42-81. Analysis revealed that women with insulin resistance ate diets of higher GL compared to women free of insulin resistance.

Also, a 15 unit increase in GL dietary value was associated with a more than doubling in risk of insulin resistance.

The authors of this study state that their results support the concept that diets with a higher GL are associated with an increased risk of insulin resistance adding Further studies are required to determine whether reducing the glycaemic intake, either by consuming lower GI foods or through smaller serves of carbohydrate, can contribute to a reduction in development of insulin resistance and long-term risk of type II diabetes.

I find it refreshing to see researchers suggest that limiting carbohydrate in the diet might be a worthy strategy for protection against insulin resistance and type 2 diabetes. All too often, the recommendation here is to eat a diet low in fat, mainly on the basis that ‘fat is fattening’, and excess weight increases the risk of insulin resistance and type 2 diabetes. I do think it’s worth bearing in mind that:

1. insulin resistance and type 2 diabetes are conditions principally of the handling of carbohydrate in the body (not fat)

2. low-carb diets generally out-perform low-fat ones regarding measures of blood sugar control and weight

Generally low GL foods to emphasise in the diet include meat, fish, eggs, nuts and green leafy vegetables.


1. O’Sullivan TA, et al. Glycaemic load is associated with insulin resistance in older Australian women. EJCN 16th September 2009 [epub before print publication]

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