Obesity and overweight are considered to be leading risk factors for a number of chronic health conditions, including diabetes mellitus, hypertension, coronary heart disease, and premature mortality. Obesity not only increases coronary heart disease risk directly, but also enhances it indirectly through its adverse effects on several established risk factors, including insulin resistance and hypertension.
Interventional studies show relatively modest weight reductions achieved with structured programs of physical activity. However, in a recent trial, cardiac rehabilitation patients randomized to an intensive counseling, and exercise program designed to achieve an energy expenditure of 3000 to 3500
kcal/wk or standard cardiac rehabilitation group, experienced double the weight loss (8.2 ± 4 versus 3.7 ± 5
Despite the relatively low exercise-induced weight reduction, findings from large epidemiological studies support the concept that reduced risk mortality occurs among more active individuals regardless of body weight [47
]. In a large follow-up study of 25
714 men, higher fitness levels were associated with lower risk of mortality in normal-weight, overweight, and obese men [48
]. In addition, the higher mortality risk associated with higher waist circumference was trivialized after adjustment for fitness [49
]. These investigators suggested that it is as important for clinicians to assess the fitness status of an overweight or obese patient as it is to evaluate blood pressure, inquire about smoking habits, and measure fasting plasma glucose and lipid levels.
Similarly, in two reports from the Nurses' Health Study (n
957 combined), after adjustment for age, smoking status, parental history of coronary heart disease, menopause, hormonal use, and alcohol consumption, higher levels of physical activity in women were associated with reduced mortality risk across all categories of body weight [50
]. It is noteworthy that the mortality risk associated with obesity was attenuated by higher levels of physical activity, but was not totally eliminated. Similarly, being lean did not counteract the increased risk associated with being physically inactive [50
Other prospective studies performed over the last decade have assessed the independent and joint associations between body weight, fitness, physical activity patterns, and outcomes. The findings of these studies support that both physical inactivity and excess weight are independently associated with the increased risk of cardiovascular disease [52
]. However, a consistent finding of these studies is that fitness attenuated mortality risk regardless of body weight. When stratified within a given category of body dimensions (body mass index, waist circumference, or weight), subjects who are more physically active or fit consistently have a lower risk for adverse outcomes compared with those who are inactive or unfit.
Recent epidemiological findings have also drawn attention to an inverse association between body mass index and mortality in some populations, often termed the obesity paradox [54
]. One explanation may be that individuals within the lowest body mass index category may have had undefined chronic illness, resulting in nonvolitional weight loss [55
]. This is supported by two recent report from the Veterans Affairs database. In the first report, the inverse association between body mass index and mortality observed in male veterans was attenuated when fitness levels were considered suggesting that individuals with low body weight and low exercise capacity may have had undetected chronic disease [56
]. In the second report, weight gain over a mean follow-up period of seven years was related to lower mortality and weight loss was related to higher mortality when compared with stable weight [57