As the focus of public health nutrition switches from fats to carbohydrates there is uncertainty about how carbohydrates actually affect the risk for chronic diseases, such as type 2 diabetes and coronary heart disease. Early dietary advice on fats was based on effects on blood cholesterol but what mechanisms are driving the risk associated with carbohydrate?

Glycaemic response or fructose?

One view is that the key driver of carbohydrate-related risk is glycaemic response i.e. the degree to which carbohydrates raise blood glucose and insulin levels. If glycaemic response is the critical factor then the dietary measure of interest would be glycaemic load, which takes into consideration both the amount of carbohydrate consumed and its potential to raise blood glucose.

An alternative view is that fructose drives the chronic disease risk associated with dietary carbohydrate. If so, we should expect fructose or perhaps sucrose (the major dietary source of fructose) to be associated with risk for chronic disease in large population studies. And, importantly, glycaemic load would not be linked with risk.

Let’s look at the epidemiology and see if it supports one argument or the other.

Glycaemic load and coronary heart disease risk

Four meta-analyses of prospective cohort studies of glycaemic load and risk for coronary heart disease have been published in the last couple of years (Dong 2012, Fan 2012, Ma 2012, Mirrahimi 2012). The findings are essentially the same – glycaemic load is associated with heart disease in women but not men. In two of the meta-analyses the links between glycaemic load and heart disease were stronger in overweight subjects. Fan (2012) also found an association with stroke incidence, as did Sieri (2013) in a recent cohort study. In all four meta-analyses the relative risks for heart disease in men were positive – they just failed to reach statistical significance, perhaps due to smaller numbers.

A study in a Chinese cohort published last year found glycaemic load was associated with coronary heart disease risk in both genders (Yu 2013). Compared to studies in western populations carbohydrate intake was high (68% of calories) but sugar intake was relatively low. Most of the carbohydrate was starch, 87% of which came from white rice and refined wheat products.

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Canadian professor Tom Wolever has provided a spirited argument for the adoption of glycaemic index as a measure of carbohydrate quality, lining it up against wholegrains. Which approach should be preferred?

Those who have been following the carbohydrate quality debate will enjoy a recent feisty review by Professor Tom Wolever from the University of Toronto published in the European Journal of Clinical Nutrition. Wolever is the co-inventor of the glycaemic index concept and is obviously a little peeved that other measures of carbohydrate quality such as wholegrain have gained acceptance in dietary guidelines whereas GI has not.

Wholegrains versus GI

Here is how Wolever weighs up the relative merits of wholegrains and GI as measures of carbohydrate quality (minimally edited).

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