Dose-response effect of walking exercise on weight loss. How much is enough?

OBJECTIVE: Exercise is the cornerstone of behavioral weight loss programs. The total volume of exercise needed to both promote weight loss and elicit health benefits has not been sufficiently investigated. The aim of this study was to examine the effects of two different volumes of walking 'metabolic fitness' exercise prescriptions, in combination with a low-fat, ad libitum diet (LFAL) on weight loss and additional modifiable health-related variables (HRV) in an ethnically diverse sample of overweight premenopausal women. DESIGN: Clinical 12 week weight loss intervention study with a 5.0-5.8MJ diet daily with (a) participants walking 30min, 5 days per week (DEX1), (b) participants walking 60 min, five times per week (DEX2) or (c) a diet only control group (DO). SUBJECTS: A mixed racial sample (predominantly Hispanic) of 56 subjects (mean BMI=34.26 +/- 6.61, mean age= 39.45 +/- 7.34) completed the 12 week program. MEASUREMENTS: Various body weight, body composition and fat distribution variables, dietary intake and additional HRV such as blood lipids, blood pressure and an estimate of cardiorespiratory fitness at baseline and after 3 months. RESULTS: All groups showed similar and significant (P < 0.001) declines in body weight, percentage body fat, BMI, WHR, fat mass, fat-free mass and diastolic blood pressure following the program. In addition, total cholesterol, triacylglycerol and the TC:HDL ratio displayed a significant time effect (P < 0.05). Significant interactions (P < 0.05) were found for waist circumference, sagittal diameter, estimated VO2max and LDL-C, with both exercise groups showing similar and significantly greater (P < 0.05) improvements than DO. Significant interactions (P < 0.05) ere also observed for several dietary variables. CONCLUSION: Our study showed no dose-response effect of walking exercise on weight loss over diet alone. Both lower and higher volume metabolic fitness prescriptions resulted in similar and significant beneficial changes in several HRV. This data suggests that 30 min of walking on most days of the week may be as beneficial as 60 min (in combination with diet) in promoting numerous additional healthful outcomes over diet alone following a 12 week weight loss program.