ALTERATIONS IN FUEL SELECTION AND VOLUNTARY FOOD-INTAKE IN RESPONSE TO ISOENERGETIC MANIPULATION OF GLYCOGEN STORES IN HUMANS

This study investigated the relative importance of alterations in carbohydrate intake or oxidation as mechanisms for rectifying extreme perturbations of glycogen stores. Six lean men were studied on three occasions in which a stabilization period (days 1 and 2) was immediately followed by whole-body indirect calorimetry (days 3-5). Glycogen stores were manipulated on days 3 and 4 by using isoenergetic diets providing carbohydrate at 79% (HC), 48% (MC), or 9% (LC) of energy. Free access to MC meals and snacks was allowed on days 5 and 6 outside the calorimeter. The manipulations caused large alterations in glycogen stores (HC, +206 g; MC, +132 g; LC, -121 g; HC vs LC, 327 g), but subsequent voluntary food intake was very similar across treatments (HC, 18.2 MJ/36 h; MC, 17.7 MJ/36 h; LC, 18.1 MJ/36 h, NS). Over days 3-5 the average difference in carbohydrate intake (HC vs LC) was 16.1 MJ (1010 g), but balances differed by only 1.7 MJ (110 g) because of autoregulatory changes in carbohydrate oxidation. These were the only significant mechanisms for reestablishing carbohydrate balance.