Can Thinner Mean Sicker? Obesity Paradox

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High body fat and high lean mass index were independently associated with reduced mortality at 3 years.

The observation that obesity may aid survival in patients with some chronic diseases — the obesity paradox — cannot be explained away by a presumed “flaw” in the body mass index metric.

In a study of 570 coronary artery disease patients, death was more likely to come to skinny patients compared with those who had more fat than lean mass, according to Carl J. Lavie, MD, of the John Ochsner Heart & Vascular Institute in New Orleans, and colleagues.

The study, which was published by the Journal of the American College of Cardiology, revealed a 15 percent mortality rate among patients with low body fat and a low lean mass index (LMI), compared with a 2.2 percent mortality rate in patients with high body fat/high LMI.

“People have said the body mass index is not accurate because it doesn’t always represent true fat,” Lavie told MedPage Today. “But we have shown using different body composition metrics that the obesity paradox is present in patients with stable coronary heart disease.”

In a logistic regression analysis, both low body fat and LMI as categoric variables were independent predictors of 3-year mortality.

And the converse of that was also true: high body fat and high LMI as categoric variables each were independently associated with reduced mortality at 3 years.

Low body fat as a continuous variable was a significant predictor of mortality, while low LMI as a continuous variable was not.

It’s not that being overweight or obese is good for the heart, but once overweight and obese individuals get heart disease, their prognosis seems to be better than their skinnier counterparts, Lavie explained.

“The person who is in trouble is the thin person who develops heart disease. Physicians should pay closer attention to their increased mortality risk and try to attenuate it,” Lavie said.

Although the exact mechanism supporting the obese paradox is not fully understood, Lavie said there is some evidence that muscular strength plays a role.

“Although we didn’t look at this, my prediction is that the patients with high body fat and high lean mass would have higher muscular strength as well,” he said, noting that genes also play a role.

The researchers evaluated 570 consecutive patients with coronary heart disease who were referred to cardiac rehabilitation between 2000 and 2005. During the 3-year follow-up, 26 patients died.

The average BMI for those with low body fat/low LMI was 22, versus 32 for those with high body fat/high LMI.

At baseline, compared with survivors, those who died had significantly lower BMI (25.1 versus 28.7), body fat (25.2 versus 29.6), LMI (18.5 versus 20), ejection fraction (42.9 percent versus 55 percent), and peak oxygen flow (12.4 versus 16.9 mL/kg/min). They also had borderline lower levels of systolic blood pressure.

However, those who died were significantly older than survivors (72 versus 63).

Those with the lowest LMI had a higher mortality rate (10.3 percent) compared with those in the highest LMI group (2.7 percent). Similarly, a low body fat combined with a low LMI conferred a higher risk of death than a high body fat combined with a high LMI (15 percent versus 2.2 percent).

Interestingly, even though a high body fat was associated with better survival, these patients tended to have a worse overall cardiovascular risk profile, researchers noted, which included lower HDL cholesterol, higher triglycerides, and higher C-reactive protein.

Those with chronic obstructive pulmonary disease had a higher risk of death, but these patients also had lower body fat and lower LMI.

The study has some limitations, according to the authors, including its retrospective nature, and the relatively small cohort and short follow-up.

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