Exercise, appetite and energy balance
Obesity, through a persistent positive energy and fat balance is of major public health significance due to its detrimental health, social and financial costs. Increasing physical activity levels through recreational exercise and decreasing energy intake have been implicated with obesity prevention. However, the addition of exercise to normally sedentary routines will only prevent positive energy balance if it is not tracked b a compensatory response in energy intake and non-exercise physical activity [also termed non-exercise activity thermogenesis (NEAT)]. The current series of studies set out to examine the quantitative and temporal relationship between exercise and energy balance with specific reference to appetite, energy intake and NEAT. These studies were designed using similar methodologies that could be compared and related to existing studies. The results showed that in younger motivated individuals, moderate-high intensity mandatory exercise increased daily energy expenditure leading to a marked negative energy balance. However for periods of up to two weeks, analysis of temporal trends revealed evidence of compensatory changes to re-establish energy balance (re-equilibrium phase). This re-equilibrium was a result of not only increases in energy intake, but also (and to a greater extent) decreases in NEAT. Inter-individual variability in the extent of compensation was evident and independent of age, sex, BMI and restraint status. Decreases in physical activity did not lead to a compensatory reduction in energy intake and lead to a marked positive energy balance. Using an exercise intervention, in line with government guidelines, in a group venerable to becoming obese showed that body mass was largely unaffected since overall energy expenditure was not significantly elevated, primarily due to a lack of motivation to reach the required exercise prescription. The results have public health significance in the formation of policy to increase physical activity in the population.