What is obesity paradox?

There are several observations which have shown that in the elderly and patients with chronic diseases like heart failure and coronary artery disease, overweight or mild obesity may be protective and is associated with higher survival. That could be because of lack of discriminatory power of body mass index to differentiate between body fat and lean mass [1]. That systematic review of 40 cohort studies with over 250 thousand patients with coronary artery disease had a mean follow-up period of 3.8 years. Those with body mass index below 20 had increased relative risk of total mortality and cardiovascular mortality. Overweight patients with BMI between 25 and 29.9 had the lowest risk for total mortality and cardiovascular mortality.

Obesity paradox has also been noted in heart failure patients with ejection fraction of 35% or less who have been given an implantable cardioverter defibrillator. Among the 904 patients with mean age of 67 years in a study, 26% had normal BMI while 32% were overweight and 42% were obese. Even though there was higher prevalence of diabetes, hypertension and prior myocardial infarction in the obese and overweight groups, mortality was lower at 10.1% and 7.9% respectively, than in the normal BMI group with a mortality of 22.9% (P<0.001).

Some explanations have been put forward to explain the obesity paradox. One is lead time bias, that is patients with obesity may develop cardiac disease earlier in their lifetime. Earlier age at the time of diagnosis of cardiac disease may mean lower comorbidity burden, contributing to the better outcome. Another reason is that cardiac cachexia may be the reason for low BMI and unintentional weight loss with associated high mortality rate [3].

References

1. Romero-Corral A, Montori VM, Somers VK, Korinek J, Thomas RJ, Allison TG, Mookadam F, Lopez-Jimenez F. Association of bodyweight with total mortality and with cardiovascular events in coronary artery disease: a systematic review of cohort studies. Lancet. 2006 Aug 19;368(9536):666-78. doi: 10.1016/S0140-6736(06)69251-9. PMID: 16920472.
2. Jahangir A, Mirza M, Shahreyar M, Mengesha T, Shearer R, Sultan S, Jahangir A, Choudhuri I, Nangia V, Dhala A, Bhatia A, Niazi I, Sra J, Tajik AJ. Presence of obesity is associated with lower mortality in elderly patients with implantable cardioverter defibrillator. Int J Obes (Lond). 2018 Feb;42(2):169-174. doi: 10.1038/ijo.2017.211. Epub 2017 Aug 30. PMID: 28852203.
3. Holmstrom L, Junttila J, Chugh SS. Sudden Death in Obesity: Mechanisms and Management. J Am Coll Cardiol. 2024 Dec 3;84(23):2308-2324. doi: 10.1016/j.jacc.2024.09.016. Epub 2024 Nov 6. PMID: 39503654.