Body weight control is thought to be improved when physical activity and energy intake are both high (high energy turnover (ET)). The aim of the present study was to investigate the short-term impact of ET on fat balance during zero energy balance (EB), energetic restriction (ER) and overfeeding (OF). In a randomised crossover study, nine healthy men (BMI: 23·0 (SD 2·1) kg/m2, 26·6 (SD 3·5) years) passed 3 × 3 d in a metabolic chamber: three levels of ET (low, medium and high; physical activity level = 1·3−1·4, 1·5−1·6 and 1·7−1·8) were performed at zero EB, ER and OF (100, 75 and 125 % of individual energy requirement). Different levels of ET were obtained by walking (4 km/h) on a treadmill (0, 165 and 330 min). Twenty-four-hour macronutrient oxidation and relative macronutrient balance (oxidation relative to intake) was calculated, and NEFA, 24-h insulin and catecholamine secretion were analysed as determinants of fat oxidation. During EB and OF, 24-h fat oxidation increased with higher ET. This resulted in a higher relative fat balance at medium ET (EB: +17 %, OF: +14 %) and high ET (EB: +23 %, OF: +17 %) compared with low ET (all P < 0·05). In contrast, ER led to a stimulation of 24-h fat oxidation irrespective of ET (no differences in relative fat balance between ET levels, P > 0·05). In conclusion, under highly controlled conditions, a higher ET improved relative fat balance in young healthy men during OF and EB compared with a sedentary state.

The present study aimed to investigate whether substrate metabolism, appetite and feeding behaviour differed between high and low energy turnover conditions. Thirteen overweight premenopausal women completed two 1 d trials: low energy turnover (LET) and high energy turnover (HET), in a randomised, cross-over design. In LET, subjects consumed a test breakfast (49 % carbohydrate, 37 % fat, 14 % protein) calculated to maintain energy balance over a 6 h observation period, during which metabolic rate and substrate utilisation were measured and blood samples taken. Immediately following this an ad libitum buffet meal was provided. HET was identical to LET, except that subjects walked on a treadmill for 60 min at 50 % VO2max before the test breakfast, which was increased in size (by about 65 %) to replace the energy expended during the walk and maintain energy balance over the observation period. Postprandial fat balance (i.e. the difference between fat intake and oxidation) was lower and carbohydrate balance higher in HET compared with LET throughout the postprandial period (P < 0·05 for both). After the buffet meal, carbohydrate balance did not differ between trials but energy and fat balances were lower (by 0·28 MJ and 11·6 g, respectively) in HET compared with LET (P < 0·001 for both). Carbohydrate balance immediately before the buffet meal correlated negatively with buffet energy intake (r − 0·49) and postprandial acylated ghrelin responses (r − 0·48), and positively with postprandial glucose responses (r 0·49). These findings demonstrate that HET resulted in a more positive carbohydrate balance than LET, which associated with lower subsequent energy intake. This may have implications for the regulation of body weight.