The subject of energy balance in humans has been well researched over the past one hundred years. However, the reason why some individuals are better at regulating their body weight than others is still far from clear. The aim of this study was to further investigate the relationship between energy expenditure and energy intake under varying conditions. The first phase involved a set of three experiments. Experiment 1 (n=15, men) was based on expending energy through exercise (EX)(837 kJ on a cycle-ergometer), exercise in the cold (11-13°C) (CES), exercise with prior caffeine (200mg) ingestion (CAFF) and a control condition (CS). Experiment 2 compared two levels of energy expenditure with a control (CT) in 12 men (a) 837 kJ (LIE) and (b) 2510kJ (HIE). In experiment 3, subjects undertook two tests: an exercise session 837 kJ and a control condition. Subjects in experiment 3 were categorised into three groups according to their 8MI: lean (L, n=6), normal weight (NW, n=13) and overweight (OW, n=13). Analysis of data from experiment 1 showed no significant difference in energy intake for the four conditions: 5.7(±1.2), 5.7(±1.6), 5.6(±1.4) and 6.0(±1.6) MJ for CS, EX, CAFF and CES conditions respectively. A significant increase in energy intake only in the HIE condition compared with the CT (p =0.028) was observed in experiment 2. In experiment 3, energy intake for the Land NW subjects were in concordance between the exercise and control conditions (rs=0.943, p =0.005 and rs=0.797, p=0.001 respectively) but not for the OW subjects (rs= 0.258, p=0.394). A significant increase was observed in 12-hour energy intake between the test conditions and habitual for the OW subjects (p=0.014) but not for the Land NW subjects. The second phase investigated the effect of hot peppers on energy expenditure after ingestion - post-prandial thermogenesis (PPT) in 17 men. Findings confirmed that a significant increase in PPT (27%) occurred after a hot pepper meal compared with the control (p