Low-fat diets produce spontaneous weight loss in the research setting, but as a public health strategy, they have been disappointing. Insulin resistance and impairments in insulin secretory function leading to postprandial hyperglycaemia are now common, making the current context greatly different to that of 25 years ago. There is increasing evidence that reducing the proportion of energy derived from carbohydrate or reducing the glycaemic index (GI) of the carbohydrate improves the rate of fat loss and cardiovascular risk factors. The proposed mechanisms include higher satiety, higher metabolic rate, reduced postprandial glycaemia and/or insulinaemia and higher fat oxidation. Although dietary glycaemic load can be reduced either by lowering the GI of the carbohydrate or by reducing carbohydrate energy, the metabolic and physiological consequences are not the same. Exchanging high for low-GI foods, without changing the macronutrient ratio, may be optimal because it is simple, cost-effective and often associated with higher intake of whole grains and greater food volume, and factors that maximize the chance of sustained weight loss. Healthy low-GI diets allow for moderate intakes of sugars, including sweetened dairy foods, fruits and confectionery items, and can be easily adapted for individuals of different ethnicities, vegetarians and low-income groups.Keywords: glycaemic index, glycaemic load, carbohydrate, weight loss, insulin resistance