Study: The 'Obesity Paradox,' Wherein Being Overweight Appears to Help

A massive study out of Sweden finds that after heart attacks, obese patients had better subsequent survival rates than those with normal body mass indices.


Jessica Rinaldi/Reuters

PROBLEM: Since 1999, researchers have been investigating the "obesity paradox," a phenomenon that finds overweight patients with certain chronic diseases having better odds of survival than their less heavy (and therefore, we are predisposed to presume, healthier) counterparts. The difficulty in seeing obesity as anything but a health liability has, as the authors of this study point out, oftentimes lead doctors to recommend weight loss as a veritable cure-all. There is less understanding of when losing weight might not, in fact, be in an overweight patient's best interest. This particular study evaluated the relationship between BMI and mortality in patients with heart disease, with the stated purpose of evaluating whether the obesity paradox could be observed in this population.

METHODOLOGY: The largest of its kind, this study analyzed data from 64,436 adults on the Swedish Coronary Angiography and Angioplasty registry who had been diagnosed with acute coronary syndromes (ACS) -- angina or heart attacks. Researchers divided the patients into 9 categories based on their BMI, ranging from underweight (having a BMI under 18.5) to obese (having a BMI over 35). Controlling for potentially confounding variables, they evaluated the overall mortality of patients with significant stenosis, or narrowing, in one or more coronary arteries over an average follow-up period of 21 months.

RESULTS: Overweight patients, with a BMI of 26.5 to 28, had the lowest risk of dying. Death risk decreased as BMI increased up until BMIs began to creep past 40, in which case the risk of dying once again increased -- this can best be visualized as a U-shaped curve, where being overweight is associated with the lowest rate of mortality. This pattern remained consistent across differences in age, sex, and treatment method, and for patients who had been treated with percutaneous coronary interventions (PCIs), being underweight was associated with a three times greater death risk than being overweight.

CONCLUSION: For up to three years after hospitalization, overweight and obese patients with acute coronary syndromes had a lower mortality rate than patients with BMIs in the normal range. The obesity paradox holds, it would seem, for the prognosis of patients diagnosed with heart disease.

IMPLICATIONS: This study does not establish a causative relationship between excess weight and reduced mortality. The authors cannot explain the mechanism behind the trend that they identified, but it has previously been argued that confounding factors may be contributing to the lowered mortality of obese populations with chronic diseases. It has also been put forth that unidentified biological pathways protect obese patients with heart disease from premature death, and that an excess of fat is possible a beneficial source of energy to bodies in distress. It is worth reiterating as well that this these results do not suggest that having a higher BMI lessens one's risk of developing heart disease in the first place. Still, an accompanying editorial maintains that enough data now exists for us to conclude that weight loss should never be recommended for patients with chronic illness and a BMI under 40.

LIMITATIONS: Until causative factors are identified, the authors caution that the study's limitations -- that the patient group was predominantly white, that suffering a heart attack might have inspired overweight patients to follow a more healthy lifestyle, or that BMI isn't a perfect measure of obesity -- prevent it from being a definitive endorsement of the "obesity paradox."

The full study, "Evidence for obesity paradox in patients with acute coronary syndromes: a report from the Swedish Coronary Angiography and Angioplasty Registry ," will be published in the European Heart Journal.