A meta-analysis of the past 25 years of weight loss research using diet, exercise or diet plus exercise intervention

OBJECTIVE: The therapeutic effectiveness of diet, exercise, and diet plus exercise for weight loss in obesity was determined. DATA SOURCES: All human research reported in English, published in peer-reviewed scientific journals within the past 25 y was reviewed. STUDY SELECTION: Acceptance criteria (n=493 from>700 studies) were that a therapeutic intervention of diet, exercise or diet plus exercise was employed, specifically for weight reduction in obese adult humans and that weight change was reported numerically. Only aerobic exercise studies were included, while drug, hormone and surgical treatments were excluded. DATA EXTRACTION: All data were extracted by the same investigator from the original research report. Except for gender and program type, all extracted data were numerical. DATA SYNTHESIS: ANOVA, with a Newman–Keuls post hoc test, was used to determine differences among programs (P<0.05). One analysis was performed on the group mean data and one based on effect sizes. Analyses were repeated using initial body weight, initial percent body fat and program length, as covariates. RESULTS: Primarily, subjects aged 40 y have been studied (39.5±0.4 y, mean±s.e.m.) who are only moderately obese (92.7±0.9 kg, 33.2±0.5 body mass index (BMI), 33.4±0.7% body fat); for short durations (15.6±0.6 weeks). Exercise studies were of a shorter duration, used younger subjects who weighed less, had lower BMI and percentage body fat values, than diet or diet plus exercise studies. Despite these differences, weight lost through diet, exercise and diet plus exercise was 10.7±0.5, 2.9±0.4* and 11.0±0.6 kg, respectively. However, at one-year follow-up, diet plus exercise tended to be the superior program. Effect size and covariate analyses revealed similar program differences. CONCLUSION: Weight loss research over the past 25 y has been very narrowly focused on a middle age population that is only moderately obese, while the interventions lasted for only short periods of time. The data shows, however, that a 15-week diet or diet plus exercise program, produces a weight loss of about 11 kg, with a 6.6±0.5 and 8.6±0.8 kg maintained loss after one year, respectively.