Carbohydrate balance and body-weight regulation

Carbohydrates generally provide 4040% of the total food energy, and daily carbohydrate intakes in adults consuming mixed diets range from 200 g in relatively small and sedentary individuals to more than 500 g in physically-active adults. The body's glycogen reserves (Bjorntorp & Sjostrom, 1978) can be presumed to be not much greater than the amount of carbohydrate consumed and oxidized during a typical day. Given the small size of this fuel reserve in relation to its turnover, maintenance of appropriate glycogen stores and blood glucose levels presents a considerable challenge to metabolic regulation, but even large variations in carbohydrate intake can be accommodated without noticeable stress and while keeping up usual functions and activities (Stubbs et al. 1995~). Evidently, glucose oxidation adjusts itself to carbohydrate availability quite effectively. Maintenance of appropriate glycogen levels under conditions of ad lib. food intake would be facilitated if, in addition to adjustment of glucose oxidation to carbohydrate intake, food intake were to be regulated in a manner helping to sustain the balance between the use of glucose and the influx of dietary carbohydrate (Flatt, 1987). Making these considerations at a time when the existence of specific glucose receptors in the brain had just been revealed, Indeed, it is now known that transient small declines in blood glucose levels tend to elicit feeding (LeMagnen, 1981; Campfield & Smith, 1990). However, blood glucose levels vary greatly during the day, and there is much overlap between the values that prevail under very different nutritional and metabolic conditions. Subsequently, it was considered, therefore, that changes in liver glycogen levels In the following discussion I will attempt to delineate how the need to maintain carbohydrate balance contributes to the regulation of food intake and thereby to the control of body weight.