Much interest has been focused on the relationship between glycaemic index and body-weight loss, some of which is fueled by popular media. However, there is a number of potential mechanisms that could be triggered by reducing the glycaemic index of the carbohydrate consumed in the diet. For example, the effect of foods on the gastrointestinal tract and the effect on blood glucose both could lead to potential appetite effects. Acute meal studies seem to point to an effect of glycaemic index on appetite regulation. However, the results of longer-term studies of weight loss are not as clear. In the present review a possible reason for this variation in outcome from the weight-loss studies will be discussed. The present review focuses on the possibility that the fermentable fibre content of the low-glycaemic-index diet may be important in weight-loss efficacy. A novel receptor that binds SCFA, the products of carbohydrate fermentation, has recently been described on the enteroendocrine L-cell in the colon. This cell releases a number of anorectic hormones and could offer an explanation of the appetite suppressant effects of fermentable carbohydrates. It could also explain the variability in the results of glycaemic-index weight-loss studies.