Purpose: The purpose of this review was to address three specific questions. 1) Do higher levels of physical activity attenuate the increased health risk normally observed in overweight or obese individuals? 2) Do obese but active individuals actually have a lower morbidity and mortality risk than normal weight persons who are sedentary? 3) Which is a more important predictor of mortality, overweight or inactivity?
Methods: We initially identified more than 700 articles that included information on the exposure variables of body habitus (body mass index, body composition, or body fat pattern) and physical activity habits, and on outcomes such as morbidity or mortality. To be included in the review, we required that an article include an analysis of one of our outcomes by strata of the two exposure variables. We excluded review articles and reports of cross-sectional analyses. We used an evidence-based approach to evaluate the quality of the published data.
Results: We summarized results from 24 articles that met all inclusion criteria. Data were available for the outcomes of all-cause mortality, cardiovascular disease mortality, coronary heart disease (CHD), hypertension, type 2 diabetes mellitus, and cancer. Summary results for all outcomes except cancer were generally consistent in showing that active or fit women and men appeared to be protected against the hazards of overweight or obesity. This apparent protective effect was often stronger in obese individuals than in those of normal weight or who were overweight. There were too few data on cancer to permit any conclusions.
Conclusions: There are no randomized clinical trials on the topics addressed in this review. All studies reviewed were prospective observational studies, so all conclusions are based on Evidence Category, C. The conclusions for the three questions addressed in the review are: 1) regular physical activity clearly attenuates many of the health risks associated with overweight or obesity; 2) physical activity appears to not only attenuate the health risks of overweight and obesity, but active obese individuals actually have lower morbidity and mortality than normal weight individuals who are sedentary, and 3) inactivity and low cardiorespiratory fitness are as important as overweight and obesity as mortality predictors. Research needs include extending current observations to more diverse populations, including more studies in women, the elderly, and minority groups, assessment methods need to be improved, and randomized clinical trials addressing the questions discussed in this review should be undertaken. Owing to size, complexity, and cost, these trials will need to be designed with valid noninvasive measures of subclinical disease processes as outcomes.