The obesity paradox in heart failure— the finding that obesity has been associated with lower mortality in some heart failure studies — is no longer novel, but it remains incompletely understood. Nevertheless, appreciation of this paradox has important clinical implications, given the high prevalence of obesity among patients with heart failure.
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Such appreciation is particularly helpful when advising patients with (or at risk of) heart failure about weight management and cardiorespiratory fitness, as the latter appears to be a major factor influencing the obesity paradox. That’s the premise of a recent review in the Cleveland Clinic Journal of Medicine (2021;88:449-458) by Luke Laffin, MD, and Erik Van Iterson, PhD, MS, of Cleveland Clinic’s Miller Family Heart, Vascular & Thoracic Institute, along with recent Cleveland Clinic resident Asad Khan, MD.
“Obesity increases the risk of developing heart failure regardless of fitness level, but better cardiorespiratory fitness attenuates the risk,” says Dr. Laffin, a cardiologist in the Section of Preventive Cardiology and Rehabilitation.
“Weight appears to be only a part of the obesity paradox story,” adds Dr. Van Iterson, Director of Cardiac Rehabilitation. “Evidence indicates that cardiorespiratory fitness can be a significant modifier of the paradox as well.”
Essentials of BMI, fitness and the paradox
The bulk of their review article distills current understanding of the roles of cardiorespiratory fitness and body mass index (BMI) in individuals with heart failure, leading to several key conclusions:
- BMI and cardiorespiratory fitness both affect heart failure development, but fitness is likely the more significant factor.
- Increased fitness is associated with a reduced risk of heart failure hospitalization as an individual ages.
- The obesity paradox is not as consistently reported for patients with heart failure with preserved ejection fraction (HFpEF) as it is for those with reduced ejection fraction (HFrEF).
Takeaways for patients
The authors conclude their review with guidance for counseling patients as evidence on these questions continues to evolve. They begin by emphasizing two major themes that are supported by studies to date:
- Obesity and low cardiorespiratory fitness are risk factors for heart failure development.
- Obesity in people with low fitness is protective for those with established heart failure.
They note that advice beyond this is less clear, as the latest U.S. and European guidelines on heart failure offer only limited guidance on managing obesity in patients with established heart failure. Moreover, a 2018 position paper from the Heart Failure Association of the European Society of Cardiology supports cardiopulmonary exercise testing only for assessing the risk of heart failure.
Against this backdrop of scarce guidance, the authors propose a few recommendations for patients:
- For heart failure prevention, weight loss through dietary and lifestyle changes can be recommended. This recommendation stems from evidence showing that a lower BMI predicts reduced risk of heart failure development, the authors note.
- For patients with heart failure and obesity, moderate weight loss may be appropriate. Lifestyle interventions aimed at weight loss and improving cardiorespiratory fitness, such as with a phase 2 cardiac rehabilitation program, should be considered, the authors note. “Studies suggest that such interventions reduce risk by improving fitness in patients with obesity and heart failure,” Dr. Laffin explains. “And, importantly, there are no data suggesting harm.”
- For patients with established HFrEF, intentional weight loss appears to be beneficial. Patients may achieve this weight loss through lifestyle changes or bariatric surgery. Notably, unintentional weight loss appears to be detrimental in this setting, the authors point out. “When advising weight loss to patients with heart failure and obesity, it is important to consider the patient’s individual clinical profile,” Dr. Laffin observes.
What to study next
The review concludes with an overview of remaining research priorities. High on the list is better evaluation of obesity’s impact on different heart failure phenotypes. “There are distinct pathophysiologic differences between heart failure with reduced, mid-range and preserved ejection faction, with corresponding differences in therapeutic responses,” says Dr. Van Iterson. “Analyses that group all patients with heart failure together may blur results.”
A similar priority is defining BMI thresholds at which obesity’s effect shifts from protective to deleterious. “Various classes of obesity are frequently combined in studies,” Dr. Van Iterson says. The authors call for future research to examine the effect of fitness on the obesity paradox separately for individuals with class II (BMI of 35 to 39 kg/m2) versus class III (> 40 kg/m2) obesity.
Another key research priority is exploring differing effects of various interventions for weight reduction in the context of the obesity paradox in heart failure. “Future studies should assess relative risk reduction of specific exercise training combined with metabolic surgery or pharmacotherapy-induced weight loss in patients with heart failure,” the authors conclude.
The full open-access review article is available here.