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We appreciate the opportunity to respond to the insightful comments from Drs Morales Salinas and Coca, who suggest that ergo-anthropometric assessment of obesity may be preferable to the standard body mass index (BMI) method. Along with our colleagues at Ochsner Clinic and Mayo Clinic, we have been extremely interested in the current epidemic of obesity that is profoundly affecting many aspects of health in westernized societies.1,2
Although BMI is the most common method to define overweightness and obesity in both epidemiological studies and major clinical trials, clearly this method does not necessarily reflect true body fatness, and BMI/body fatness may differ considerably among people of different age, sex, and race.1,3-6 Defining obesity by other methods, including waist circumference, waist-hip ratio, and percent body fat assessment, may be more accurate.1 In fact, researchers at Mayo Clinic recently reported that BMI performed suboptimally to predict obesity as defined by the World Health Organization criterion standard (body fat >25% in men and >35% in women)7 in cohorts with coronary heart disease (CHD) and in the general population.4,8 The accuracy of BMI in diagnosing obesity is limited, particularly for individuals in the intermediate BMI ranges, in men, and in the elderly. A BMI cutoff of 30 kg/m2 or greater has good specificity but misses more than half of the people with excess body fat.
Along with the obesity epidemic, we are currently experiencing a physical inactivity epidemic in most westernized societies.9 Although both obesity and physical inactivity/reduced cardiorespiratory fitness (CRF) increase the risk of most cardiovascular diseases (CVDs), improving CRF may markedly reduce the risk of CVD among obese people.1,9,10 In fact, this latter point was made in a recent article that analyzed a large cohort of women with impaired fasting glucose or undiagnosed diabetes in which CRF, not BMI, predicted all-cause and CVD mortality.11
Researchers at both Ochsner Clinic and Mayo Clinic have also been extremely interested in the concept of the “obesity paradox.”1,12 Although clearly obesity is a major risk factor for most CVDs, numerous studies have now documented that, among cohorts with established CVD, obese cohorts surprisingly (and paradoxically) often have a better prognosis than their lean counterparts. Explaining this paradox is difficult and beyond the scope of this letter, but it has been discussed previously.1 Certainly, selection bias may play a role in the paradox. Overweight and obese persons often develop dyslipidemia, elevated blood pressure, metabolic syndrome/diabetes, increased levels of inflammation, and structural and functional alterations of the heart and vasculature that lead to substantial CVD. In fact, without weight gain, many overweight and obese patients may not have developed CVD in the first place, whereas lean patients develop CVD from a different mechanism and have a genetic predisposition, possibly making their disease more difficult to treat effectively. Part of the explanation of the obesity paradox has been blamed on the limitations of the BMI assessment of overweightness/obesity.12 Clearly, abdominal obesity has predicted all-cause and CVD mortality in all BMI categories in cohorts with end-stage renal disease.13 However, researchers from Ochsner Clinic have shown that, even when obesity is defined by the World Health Organization percent body fat method, a strong obesity paradox still exists in cohorts with heart failure and CHD, ie, those with higher percent body fat have better event-free survival.1,14,15 Despite the paradox, efforts at purposeful weight reduction have still predicted marked improvements in prognosis in cohorts with CHD.1,15,16
We agree with Morales Salinas and Coca that methods other than BMI may be better to detect overweightness/obesity and predict increased medical and CVD risk. Moreover, along with efforts at preventing obesity and promoting successful weight reduction, efforts to improve overall physical activity and CRF would go a long way to protect against CVD.