Natural sugars in foods such as bread and rice noodles can raise our insulin levels as much as the sugar that is in icecream or spooned into a cup of tea. This important revelation came to scientist Professor David Jenkins in 1981, after he conducted a series of tests on carbohydrates at the University of Toronto and recorded their impact on blood sugar.

The result was the glycaemic index (GI), which revolutionised our understanding of healthy eating by showing that some healthy complex carbs and starches can cause significant rises in insulin. The higher the GI in the foods you eat, the higher your risk of diabetes type 2 and coronary heart disease, according to several large studies from Harvard School of Public Health in the United States.

“Low-GI foods, by virtue of their slow digestion and absorption, produce gradual rises in blood sugar and insulin,” explains Professor Jenni Brand-Miller, an international expert in glycaemic index from the Human Nutrition Unit at the University of Sydney. “That’s why these foods have proven health benefits such as lowering blood fats and appetite, providing more sustained energy and reducing insulin resistance which can lead to weight gain.”

The GI lowdown

Every food on the GI has a number between 0 and 100, with foods rating as low (0–55), medium (56–69), or high (70–100). The higher the number, the faster the response on your blood sugar. Glucose scores a substantial 100, while maple syrup is rated at only 19. Honey, due to its high fructose content, which slows digestion, has a GI of 55, which is considered low to medium.

To enjoy maximum benefit from the GI, you should stick to a diet of mostly low to medium GI foods in most meals with the occasional high source thrown in. Most fruit and vegetables are low to medium GI, so they are healthy choices. You can fine-tune those choices by minimising starchy vegetables such as pumpkin/parsnip and eating more low-GI fruits such as apple rather than pineapple/apricot, which rate higher. Wholegrains, nuts and seeds, eggs, meats and dairy foods generally boast a lower GI, unlike refined grains such as crispbreads, pastries, sweet biscuits and rice crackers, which are high GI.

There are some surprising entries, though. You’d think white pasta would have a high glycaemic index, but not so. The starchy components of the flour in pasta are in such a form that they are “entrapped” so take longer to break down, leading to less of a spike in your blood sugar. Basmati rice is another interesting example: studies show it has a lower GI than both wild rice and brown rice because it contains more amylose, a starch that slows the rate of digestion.

Considered through the GI lens, foods once thought of as healthy such as potatoes and short-grain white rice have been shown to have a higher GI than white sugar and therefore cause many of the same biochemical effects in your body. Many health professionals now advise minimising the intake of high-GI foods and also taking into account the glycaemic load, which gives more information about carbohydrate amount.