The obesity paradox may be related to body composition.  

The risk of developing heart failure is increased for patients with obesity. While obesity is a recognized independent risk factor for diseases such as cancer, diabetes, and heart disease, the relationship between obesity and heart failure, an extreme form of heart disease, is complex. This complexity is evinced through a phenomenon called the “obesity paradox.” ¹ Interestingly, there seems to be a protective advantage conferred upon patients with obesity when heart failure has already been diagnosed.^1,2

Among patients with heart failure, it is reported that roughly 40 percent of heart failure patients are obese (BMI ≥ 30 kg.m2).² There is speculation that because obesity is determined by body mass index (BMI), which does not discriminate among fat mass, fat-free mass, and lean mass, patients with comparable BMI may have quite different body compositions.¹ Given that BMI does not take into account body composition measures, e.g., fat mass, fat-free mass, and lean mass, and the majority of studies do not consider body composition, diet, cardiorespiratory fitness, or waist circumference, it is possible that body composition may help explain the obesity paradox. 

BMI, Body Composition, and the Obesity Paradox 

While the risk of heart failure is elevated as BMI increases, patients with obesity and heart failure with reduced ejection fraction (HFrEF) have had better outcomes than healthy weight counterparts.¹ The reliability of BMI has been questioned in relation to adiposity, thus sparking interest in other measures such as fat vs. lean mass and the distribution of subcutaneous vs. visceral fat.² 

Researchers have talked about BMI being considered as a measure of heaviness rather than a measure of body composition.¹ A high BMI may not necessarily correlate with unhealthy fat mass. For example, professional athletes may have a higher BMI than an average adult, but they are likely to have more muscle mass and lean mass than fat mass. Additionally, a presumptively healthy weight adult may have a BMI in a healthy range but have more fat mass.¹ It’s been suggested that body composition may be a more accurate measure, especially given the critical role fat mass plays in cardiovascular disease and heart failure. 

Dual x-ray absorptiometry (DEXA), computer tomography (CT), and MRI have been used to measure body fat, but their expense, radiation exposure, and required technical expertise limits their application in clinical practice.^3,4 A less expensive and simple way to assess abdominal fat — and a well-known and long-time established predictor of cardiovascular disease — is waist circumference.² A large waist circumference has been linked to women and men (≥ 88 cm and ≥ 102 cm, respectively) with HFeEF.²

A relationship between lean muscle mass in the arms and legs and cardiovascular fitness has been suggested.¹ Patients with a higher BMI that may be in the obesity range may in fact have more lean mass in the arms and legs because of exercise, which in turns helps develop cardiovascular fitness. Patients with obesity tend to exhibit exercise intolerance and experience greater challenges in developing cardiovascular fitness as a function of exercise.¹ It is suggested that the lean mass developed as a function of exercise may not only improve cardiovascular fitness but also confer protective effects. In a study of 47,000 patients with HFeEF, lean mass was reported as offering protection, regardless of BMI.⁵  

Intentional Weight Loss in Patients with Obesity and Heart Failure

For patients with obesity, losing weight through diet and exercise is a well-documented and evidence-based strategy for managing the risks metabolic diseases and cardiovascular disease. There is currently a lack of clarity around the benefits of intentional weight loss for patients with obesity and heart failure.¹ 

Health care providers who work with patients with obesity with an elevated risk of developing heart failure should work with patients to improve cardiovascular fitness before they decompensate to heart failure.¹ Exercise will help transform fat mass to lean mass, thus reducing the risk of developing heart failure. In addition to working with patients as part of a clinically supervised exercise program, clinicians should also work with patients on other lifestyle changes such as diet. A Low Calorie Diet (LCD), Very Low Calorie Diet (VLCD), and meal replacements, when paired with exercise in a clinically supervised context, can help patients with obesity develop more lean mass and mitigate their risk of heart failure. 

Sources:

1. Obesity and heart failure: Focus on the Obesity Paradox
2. Obesity and the obesity paradox in heart failure  
3. Comparison of direct body composition assessment methods in patients with chronic heart failure
4. Assessing adiposity: a scientific statement from the American Heart Association
5. Body composition and mortality in a large cohort with preserved ejection fraction: untangling the obesity paradox