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Am Fam Physician. 2007;75(5):732

Background: Although analyses of data from the Framingham database suggest that increased body mass index (BMI) is a risk factor for the development of heart failure, recent studies have noted that obesity may be associated with better outcomes in heart failure. This has become known as the “obesity paradox.” Because these findings may lead physicians to discourage patients with heart failure from losing weight, a better understanding of the relationship between obesity and heart failure is warranted.

Results: Habbu and colleagues evaluated eight studies looking at the relationship between heart failure and BMI. All studies showed a correlation between higher BMI and survival. However, most studies had limitations such as sample size, insufficient delineation of variables used in adjustment, and the use of clinical instead of objective criteria in diagnosing heart failure; lead-time bias also was a possibility in one study. More importantly, the studies' findings suggest a negative impact from cachexia rather than positive effects from obesity. One study excluded patients with cachexia (defined as unintentional weight loss) but included patients with BMIs around 22 kg per m2, who had the same comparatively poor outcomes as the excluded patients. In another study the reverse occurred—patients with unintentional weight loss but a normal BMI remained in the study, whereas patients with very low BMIs were excluded.

Conclusion: Overall, the study results show an inverse relationship between BMI and survival, but one possible cause may be that patients were thinner because they were less healthy. In addition, the studies do not exclude the possibility that patients with very high BMIs (i.e., greater than 35 kg per m2) have worse mortality outcomes. If this is so, the U-shaped curve describing the relationship between BMI and mortality in the general population also would apply to patients with heart failure.

editor's note: This study raises questions similar to those posed by larger studies relating overweight and obesity to mortality. One study demonstrated a U-shaped curve with optimal BMIs at 25 kg per m2 and steady increases in mortality in the overweight range.1 Another study showed excess mortality in underweight and obese persons but no correlation between obesity and mortality in the overweight range (BMI = 25 to 29.9 kg per m2).2 Mortality may not be the best outcome measure because of the long lead times between morbidity and mortality and because of unhealthy conditions accounting for lower weights.—c.w.

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