The fiction of the obesity paradox

This commentary refers to ‘Anthropometric measures and adverse outcomes in heart failure with reduced ejection fraction: revisiting the obesity paradox’, by J. H. Butt et al., https://doi.org/10.1093/eurheartj/ehad083. We read, with great interest, the paper by Butt et al.,1 who found no obesity paradox in heart failure (HF), using antropometric characteristics other than body mass index (BMI). Obesity paradox is the most counter-intuitive phenomenon in HF. In essence, the concept is that increased BMI is protective and is associated with reduced mortality. Indeed, this is paradoxical: before the onset of the disease, obesity is a risk factor for its development, but once the disease is present, obesity becomes protective. In the past, we analysed the literature on obesity paradox in HF and discovered some striking similarities in the baseline characteristics of participants across the studies. Patients with higher BMI differed from normal weight patients not only by obesity but also by multiple other parameters, and differences had to be overcome by statistical methods. First and foremost, obese patients were significantly younger than their normal weight counterparts. This held true in 17 of the 19 examined studies, and in the remaining two studies, the difference was not significant.2 Second, systolic blood pressure was higher in obese subjects, favouring survival in this group. All studies, which provided actual numbers for systolic blood pressure of the participants, reported higher values, sometimes by 8–9 mmHg, in the high BMI groups. Third, the distribution of the left ventricular ejection fraction (LVEF) values among different BMI classes was also beneficial for obese group. Percentage of individuals with LVEF <30% was 32.5% in subjects with normal weight and only 18.1% in obese.3 Whenever the absolute numbers of LVEF were significantly different, they favoured obese individuals.2 Besides, obese individuals with HF had higher LVEF,2 better renal function, less prevalent and less severe valvular regurgitation, better nutritional status, and more favourable values of other indicators of wellness, including pre-albumin and cholesterol. A smaller proportion of obese patients had advanced functional class (New York Heart Association III and IV).2 Being younger and having superior cardiac function, better blood pressure, and nutritional status, obese patients, not surprisingly, had better survival. We also previously showed that not accounting for some unknown factors can result in false presumption that obesity is indeed associated with favourable outcomes, when in reality it may represent a statistical artefact.4 This unknown factor is likely the combination of favourable phenotypical features, a synergistic effect of younger age, higher LVEF, better renal function, higher systolic blood pressure, and better nutrition. To confirm our conclusion, several studies showed that the course of HF improves after weight loss,5 which is perfectly aligned with obesity being a cardiovascular risk factor, and is not compatible with obesity being favourable for survival. Supplementary data are not available at European Heart Journal online. All authors declare no conflict of interest for this contribution.