Lean Body Mass Adds New Evidence to ‘Obesity Paradox’ in CAD Patients

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Body fat alone does not appear to explain the so-called obesity paradox whereby patients with coronary artery disease (CAD) who are overweight or obese have better cardiovascular outcomes. Instead, a study published online September 5, 2012, ahead of print in the Journal of the American College of Cardiology, suggests that muscle mass may play a larger role since patients with the highest lean mass index have significantly better survival than those with little muscle and little fat.

Researchers led by Carl J. Lavie, MD, of Ochsner Medical Center (New Orleans, LA), studied 570 consecutive patients with CAD who were referred for cardiac rehabilitation. Patients were categorized as having low (≤ 25% in men and ≤ 35% in women) or high body fat and low (≤ 18.9 kg/m2 in men and ≤ 15.4 kg/m2 in women) or high lean mass index (LMI), a measure of the percentage of body weight that does not come from fat. This resulted in 4 groups of patients:

  • Low body fat/low LMI (n = 62)
  • High body fat/low LMI (n = 53)
  • Low body fat/high LMI (n = 179)
  • High body fat/high LMI (n = 276)

At 3-year follow-up, mortality was significantly higher in patients in the low body fat/low LMI group compared with all other groups. Conversely, the lowest mortality rate was seen in patients in the high body fat/high LMI group (table 1).

Table 1. Three-Year Mortality

 

Mortality Rate

P Value

Low Body Fat/Low LMI

15%

< 0.0001a

Low Body Fat/High LMI

4.5%

0.001b

High Body Fat/Low LMI

5.7%

0.0025b

High BF/High LMI

2.2%

< 0.0001b

a Comparison with other 3 groups.  b Comparison with the Low Body Fat/Low LMI group.

In multivariate analysis, both low LMI (HR 3.1; 95% CI 1.3-7.1) and low body fat (HR 2.6; 95% CI 1.1-6.4) were predictive of higher mortality, while high body fat (HR 0.91; 95% CI 0.85-0.97) and high LMI (HR 0.81; 95% CI 0.65-1.00) were predictive of lower mortality. Both surplus lean mass (OR 0.90; 95% CI 0.84-0.97) and surplus fat mass (OR 0.92; 95% CI 0.86-0.99) were independent predictors of lower mortality. There was no interaction between body fat and LMI in any of the 4 subgroups.

In addition, greater age was associated with a trend toward worse survival.

Mortality was higher among patients with COPD than those without the condition (18.5% vs. 3.9%; P = 0.004). However, in multivariate analysis, it was not an independent predictor of mortality and did not have a major effect on the impact of body fat as an independent predictor of mortality (HR 0.91; 95% CI 0.85-0.97), although it did modestly weaken the effect of LMI (HR 0.96; 95% CI 0.85-1.08).

Hypertension was associated more with high LMI (OR 1.31; 95% CI 1.00-1.69) than with high body fat (OR 1.18; 95% CI 0.82-1.69) after adjusting for age and gender, while triglycerides correlated weakly with body fat and high LMI. High C-reactive protein levels were not significantly associated with either body fat or LMI.

Putting Some Muscle in the ‘Obesity Paradox’

In a telephone interview with TCTMD, Dr. Lavie said the study is in agreement with other ‘obesity paradox’ studies showing that among patients with stable CAD, those who are overweight or obese have a better prognosis than their lean counterparts. But he said that unlike those studies, which mainly used BMI as the primary measure of body fat, this study gives a better overall picture of body fat and muscle by using LMI plus body fat, as measured by simple skin-fold assessment.

“This study shows us that lean mass is important,” Dr. Lavie said. “Just looking at BMI in these people is not enough. We were able to show here that the group that had both low lean body mass and low body fat had 7 times the mortality of the group with high lean mass and high body fat. That’s a pretty huge difference in 3-year survival. These data would certainly support the importance of efforts to improve lean body mass” in patients in the low body fat/low LMI category.

“The 2 ways that you can target and help these patients are with calorie support and exercise training with emphasis on resistance and weight training to increase the lean mass,” he added. “If you took our data literally, you could also say that there is support for improving your body fat, but I think that’s where we are seeing [simply] an association. It may not be that the obese patients are doing so much better as the fact that the very lean are doing so bad, and they are the ones we need to focus on.”

This gives rise to the idea of a ‘lean paradox,’ Dr. Lavie said, since it would be logical to think that thinner patients would be healthier and have better outcomes than those who are overweight.

“We can’t completely explain this, but we know that once these lean patients get heart disease, they do worse than those who are obese,” he said. “I think that suggests that there is a difference in causation of the heart disease itself, but we don’t know exactly what factors are involved.” 

Source:

Lavie CJ, De Schutter A, Patel DA, et al. Body composition and survival in stable coronary heart disease: Impact of lean mass index and body fat in the “obesity paradox.” J Am Coll Cardiol. 2012;Epub ahead of print.

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Disclosures
  • Dr. Lavie reports no relevant conflicts of interest.

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