Abstract
It has been hypothesized that performing aerobic exercise after an overnight fast accelerates the loss of body fat. The purpose of this study was to investigate changes in fat mass and fat-free mass following four weeks of volume-equated fasted versus fed aerobic exercise in young women adhering to a hypocaloric diet. Twenty healthy young female volunteers were randomly assigned to 1 of 2 experimental groups: a fasted training (FASTED) group that performed exercise after an overnight fast (n = 10) or a post-prandial training (FED) group that consumed a meal prior to exercise (n = 10). Training consisted of 1 hour of steady-state aerobic exercise performed 3 days per week. Subjects were provided with customized dietary plans designed to induce a caloric deficit. Nutritional counseling was provided throughout the study period to help ensure dietary adherence and self-reported food intake was monitored on a regular basis. A meal replacement shake was provided either immediately prior to exercise for the FED group or immediately following exercise for the FASTED group, with this nutritional provision carried out under the supervision of a research assistant. Both groups showed a significant loss of weight (P = 0.0005) and fat mass (P = 0.02) from baseline, but no significant between-group differences were noted in any outcome measure. These findings indicate that body composition changes associated with aerobic exercise in conjunction with a hypocaloric diet are similar regardless whether or not an individual is fasted prior to training.
Highlights
Regimented exercise is considered an important component of a structured weight loss program [1]
The purpose of this study was to investigate changes in fat mass and fat-free mass following four weeks of volume-equated fasted versus fed aerobic exercise in young women adhering to a hypocaloric diet
Subjects Subjects were 20 healthy young female volunteers recruited from a university population. This sample size was justified by a priori power analysis using a target effect size of 0.6, alpha of 0.05 and power of 0.80 with percent body fat as an outcome measure based on previously established results [17]
Summary
Regimented exercise is considered an important component of a structured weight loss program [1]. Meta-analytic data show that a combined diet-plus-exercise program is more effective in promoting long-term weight loss than a diet-only program [2]. This is consistent with a compelling body of research showing that weight management is predicated on the balance between energy expenditure and intake [3]. Since human movement alters the expenditure side of the energy balance equation, it follows that an increase in physical activity will be accompanied by a reduction in body mass provided energy intake remains constant. And importantly, there is evidence in both animal [4] and human [5] models that regular exercise can preferentially reduce abdominal fat, which has been implicated as a primary factor in cardiometabolic risk [6]. A various lipolytic enzymes compared to exercising while fed [8,16]
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