New research has strengthened the case that the glycaemic index of carbohydrate-rich foods affects the risk for cardiovascular disease and is a useful tool in weight management. But Australian health authorities are in denial, refusing to even look at the data.
Four decades ago nutritionists were taught that complex carbohydrate (starch) was desirable as it was slowly digested and absorbed, which led to a gradual rise in blood glucose and this was considered to be a good thing. In contrast, simple sugars were thought to be rapidly broken down and absorbed, giving a high blood glucose response. Although logical enough, it wasn’t true.
When the blood glucose-raising effects of various foods were actually measured it was found that some starchy foods, such as potato and rice, produced very rapid increases in blood glucose to high levels – higher than that of table sugar. Use of the terms simple sugars and complex carbohydrate is now discouraged by the World Health Organization.
Nutritionists have embraced the concept of wholegrains with a passion claiming they are protective foods. But the evidence is inconsistent, which may be due to the methodology of the studies that have been undertaken so far. As the dietary fibres found in some grain foods are beneficial for bowel function and lowering blood cholesterol there is a case for basing cereal recommendations on fibre. Other aspects of the nutritional quality of cereal goods, such as nutrient density and glycaemic index are also relevant. Just recommending wholegrains is not enough.
When it comes to recommendations about grain foods the draft Australian Dietary Guidelines keep it simple: eat mostly wholegrain. The rationale is simple too: wholegrains are nutrient-rich and protective against a range of modern diseases such as cardiovascular disease, type 2 diabetes and obesity.
But is it true? How evidence-based is this advice?
Professor Robert Lustig argues that sugar, or fructose in particular, is ‘toxic’ and increases the risk for obesity and the metabolic syndrome. He paints a simple picture – glucose is good, fructose is bad – based on the differing metabolism of these sugars. He claims that fructose is similar to alcohol and should be taxed accordingly. Professor Lustig certainly has our attention but do his claims stack up?
In last week’s blog I looked at the reviews on sugar and health conducted by the European Food Safety Authority and the US Institute of Medicine. They both found that sugar is fairly benign with respect to chronic disease but can lower the nutrient density of the diet when intake is high, though this depends on which sugar-rich foods and drinks are consumed.
Professor Robert Lustig from the University of California has a very different view.