According to the World Health Organisation, in 2011, 1.5 billion adults were estimated to be overweight worldwide with serious consequences for health. Exercise is often prescribed for weight loss in overweight/obese population. The aim of this study was to investigate the effects of a 4 weeks circuit training intervention (3d/wk, 60min/d, 70-80%HRmax) in sedentary overweight/obese and lean females on body weight control and metabolism. Importantly, subjects had been naïve to the purpose of the intervention and had been selected from population based on not being interested in weight loss. Sedentary lean (L) (n = 10, age: 22.4±4.6, BMI: 22.7±2.1kg.m-2, VO2 peak: 32.5±8.3ml.kg-1.min-1) and overweight/obese (O) (n = 7, age: 26.9±3.9, BMI: 31.1±5.6kg.m-2, VO2 peak: 26.6±7.2ml.kg-1.min-1) females finished the study. All participants completed a 3 day diet diary each week during the study including 2 weeks prior to the exercise intervention and 2 weeks post intervention which was analysed for energy and macronutrient intake. Pre and post intervention measures included peak oxygen uptake (VO2 peak), weight, body composition analyzed by Dual-Energy X-ray Absorptiometry (DEXA) and capillary blood samples for plasma leptin and adiponectin levels. Exercise dependent energy expenditure over the 4 weeks circuit training was matched between groups. Post intervention, no significant alterations (analysed by ANOVA) were observed in weight and body composition (fat and lean mass) in both groups suggesting an intact body weight set-point regulation in lean and overweight/obese. Additionally no time effects for VO2 peak were found in both groups; however, at 25 Watts overweight/ obese subjects showed a significant alteration in energy expenditure post intervention (1.15±0.38 to 1.32±0.53kcal.min-1.m-2, P<0.05) suggesting an improvement in aerobic metabolism. Respiratory exchange ratio (RER) during 50-110 watts of VO2 peak assessment was significantly higher in the overweight/obese subjects compared to the lean group (All P’s<0.05), although no changes were seen post intervention within groups. Overweight/obese participants were found to have significantly higher plasma leptin concentrations and significantly lower plasma adiponectin levels than their lean counterparts (All P’s <0.05) but no time effects were observed. Energy balance showed a trend (P<0.1) towards better regulation in both groups during and after the exercise intervention. In summary, 4 weeks exercise training of overweight/obese and lean females did not lead to weight/fat loss in subjects naïve to the purpose of the study suggesting that set point regulation is not impaired in overweight/obese female. Weight loss seen in other exercise studies might be more related to subconscious or conscious dieting than to the exercise energy expenditure.