Long-term Exercise, Weight Loss and Energy Balance

Overview

In order to examine potential gender differences in the weight loss response to exercise, the investigators propose to compare equal energy expenditure of exercise for overweight men and women using levels of exercise energy expenditure that the investigators have previously shown to prevent weight gain or promote weight loss. The investigators will randomize men and women to an exercise group, 5 days/week, for 9 months, with an energy expenditure of 400 kcal/exercise session, a group with 600 kcal/ exercise session, or a control group. 1)The investigators hypothesize that men and women randomized to sedentary control will gain weight, those randomized to 400 kcal/exercise session will maintain weight (will not gain), and those randomized to 600 kcal/exercise session will lose \~5% of body weight. 2) The investigators hypothesize there will be no differences for weight loss between genders at either 400 or 600 kcal of energy expenditure of exercise since men and women will have equal amounts of energy expenditure of exercise. 3) The investigators hypothesize that men and women randomized to 400 kcal/exercise session will completely compensate for the energy expended during exercise by altering energy intake and/or spontaneous activity and that men and women participants randomized to 600 kcal/exercise session will not completely compensate. The investigators believe the findings from this study could have important implications for exercise guidelines for weight loss.

Exercise is recommended by virtually every public health organization; however, the role of exercise is generally considered secondary to energy restriction for the treatment of obesity. Indeed, an argument can be made that suggests exercise is not effective for weight loss. Meta-analytic studies consistently find small amounts of weight loss due to exercise without energy restriction. It is critical to note that there are actually very few randomized controlled trials using exercise alone for weight loss. We believe that there are 3 critical flaws in the vast majority of the literature. 1)Participants are not supervised and is generally recorded by self report and is likely poorly estimated and in general, overestimated. 2)The amount of exercise used is usually prescribed from the guidelines for recommended levels for physical fitness and to diminish cardiovascular disease, not the amount that may be necessary for weight loss. 3)The energy expenditure of the exercise is rarely reported. Participants will be randomly assigned to expend either 400 or 600kcal per exercise session (or a control group) and will exercise 5 days per week for 9 months. All exercise sessions will be supervised and the length of the exercise session will be based upon energy expenditure (kcal/min) at a give heart rate range. To account for improvements in fitness, energy expenditure will be measured monthly and adjustments to the daily exercise prescription will be altered accordingly.