The so-called obesity paradox: real-world evidence from a national referral centre in Latin America

Background / Introduction

The obesity paradox is a counterintuitive phenomenon in which individuals with a body mass index (BMI) in the overweight or class I obesity range demonstrate better clinical outcomes than those with normal weight or with more severe degrees of obesity.

This apparent protective effect has highlighted important gaps in our understanding of obesity, suggesting the presence of complex and still poorly understood pathophysiological mechanisms.

In developing countries, socioeconomic factors contribute to highly heterogeneous populations with a high prevalence of marginalization. Consequently, there is a strong association between overweight or obesity and the development of heart failure.

Purpose

This study aim to explore the association between different degrees of obesity and cardiovascular outcomes in a contemporary Latin American population with heart failure, and to characterise the behaviour of the obesity paradox in patients with heart failure in a developing country.

Methods

We analysed data from a prospective cohort of 1,000 consecutive patients with an established diagnosis of heart failure, including all ranges of left ventricular ejection fraction. The follow-up period spanned from 2023 to 2024 and included patients who initiated chronic outpatient follow-up at our heart failure clinic.

Body mass index was measured at baseline. The primary outcome was defined as an unplanned emergency department visit due to heart failure. Patients were categorised into the following subgroups according to the conventional World Health Organization BMI classification: underweight, normal weight, overweight, and obesity.

Results

Women accounted for 302 patients (30%). Among the total cohort, 396 patients (45%) had type 2 diabetes mellitus and 451 (51%) had arterial hypertension. The predominant etiology of heart failure was non-ischaemic in 452 patients (53%).

The mean left ventricular ejection fraction was 30.3% ± 11, and the mean BMI was 26.8 ± 9.3 kg/m². According to BMI categories, there were 45 underweight patients, 334 with normal weight, 323 overweight, and 7 with obesity (≥ class I).

Using Spearman’s rho correlation analysis, a weak inverse association was observed (ρ = −0.086). A negative binomial regression model yielded an estimate of −0.011 (SE 0.0073), Z = −1.612, p = 0.107, with an incidence rate ratio (IRR) of 0.988.

Multivariate analysis demonstrated that patients with low BMI (approximately <22 kg/m²) had a higher risk of emergency department visits due to heart failure, whereas in patients with higher BMI values (25–29 kg/m²), this risk was slightly attenuated.

Conclusion

In this cohort, the relationship between BMI and the probability of emergency department visits for heart failure was non-linear, with a higher risk observed at lower BMI values and a lower risk at intermediate-to-high BMI levels. No increased risk was oberved in patients with obesity; however, obesity did not appear to confer a protective effect.U-shape patternFor image description, please refer to the figure legend and surrounding text.BMI and emergency room visitsFor image description, please refer to the figure legend and surrounding text.