Evidence suggests that physical activity (PA) may reduce the risk of several major forms of cancer. One proposed mechanism for this reduction in cancer occurrence is through the effect of PA on energy balance, specifically by creating an energy deficit. However, recent evidence suggests that there is marked individual variability in the effect of exercise on energy balance with acute studies demonstrating that some individuals significantly increase their energy intake (EI) post-exercise and are left with a positive energy balance ("compensators") while others decrease or slightly increase EI post-exercise and are left with an energy deficit ("non-compensators"). Engaging in compensatory eating behaviors following exercise could undermine the effectiveness of exercise for weight control and cancer prevention. Consequently, investigators have discussed the importance of determining the behavioral phenotype of "compensators" and "non-compensators" and efforts have already begun in this direction. However, one concern with this future research path is that we currently do not know whether an individual's EI response to exercise is consistent over time. That is, does someone who eats significantly more after exercise always eat that much more after an exercise bout? Therefore, the primary aim of this study is to determine whether one's acute EI response to exercise is consistent over time. We propose to examine 30 overweight/obese women, each of whom will participate in 3 pairs of testing sessions, with each pair consisting of an exercise (30 minutes of moderate-intensity walking) and resting (seated for 30 minutes) testing day, separated by 48-96 hours. Energy intake will be measured using an ad-libitum buffet meal served 1 hour post-exercise/rest. Following the completion of each of the 3 pairs of testing sessions, the mean difference in EI (EIdiff = EIex - EIrest) from each pair will be calculated and an intraclass correlation will be usd to examine whether the EIdiff is consistent within individuals over time. The examination of the consistency in acute EI responses to exercise can help shape the next series of studies on the effect of exercise on energy balance. If our hypothesis is supported and one's acute EI response to exercise is consistent, we can begin to examine the important clinical question of whether individual responses to chronic exercise (i.e., weight loss vs. weight gain) can be predicted from EI responses from 1 pair of testing sessions. That is, if an individual gains weight with exercise training, is this due to repeated increases in EI acutely following an exercise bout? In addition, future studies could begin to examine whether there are physiological, behavioral, and cognitive factors that predict whether an individual will increase or decrease EI post-exercise. Alternately, if our hypothesis is not supported, findings from our study can be used to power larger studies which examine whether differences in participants'responses to an exercise session (e.g., changes in affect, hunger, fatigue, etc.) contribute to higher or lower EI post-exercise.
The importance of exercise for weight control and cancer prevention is well documented;however if exercise results in an increase in energy intake, the beneficial effect of exercise may not be seen. This study addresses a gap in the current literature and examines the individual variability in energy intake responses to acute exercise and also examines whether these responses are consistent over time. A better understanding of the interrelationship between exercise and energy intake will ultimately lead to future studies that can address the clinically significant question of why some individuals gain weight and others lose weight when engaging in exercise training programs and help to develop exercise programs that maximize the effect on body weight and cancer control.