The ‘obesity paradox’ describes the inverse association that has been observed between body mass index and mortality in subjects who already have coronary artery disease. This may be because body mass index is not the most relevant biological measure of body fat in this specific patient population. Coutinho et al have recently published findings of a study that tested this hypothesis and, in particular, investigated whether central obesity may have more direct pathological relevance. The investigators performed a systematic review of the published literature and then brought together original subject data from four of the studies with detailed information on anthropometry in coronary disease patients. They combined this with unpublished data from a cardiac rehabilitation programme, which allowed them to perform a collaborative analysis across Europe, America and Asia based on 15,923 patients.
As previously observed, in this group of patients, increased body mass index was associated with reduced mortality (HR 0.64 95%CI 0.59 to 0.69). However, increased central obesity was associated with increased mortality (HR 1.70 95% CI 1.58 to 1.83). Furthermore, even in those with normal BMI, the increased risk associated with higher central obesity was the same (HR 1.70 95%CI 1.52 to 1.89). Subgroup analysis suggested the size of the effect of central obesity on mortality was similar in different risk factor groups, such as smokers and non smokers, and did not vary between men and women. The authors point out in the discussion that ‘…central obesity alone explained approximately 30% of all deaths’. They add that these findings highlight the importance of assessing body fat distribution, by measuring waist circumference and waist to hip ratio, even in coronary disease patients with normal BMI, in order to assess risk accurately.