key: cord-0858308-zx78qhe5
authors: Samuels, Jon D.; Lui, Briana; White, Robert S.
title: Clearing up the obesity paradox in cardiac surgery
date: 2020-06-23
journal: J Cardiothorac Vasc Anesth
DOI: 10.1053/j.jvca.2020.06.057
sha: 26d3de01cfb8f668fc0c4bc6496995ca03ac56e8
doc_id: 858308
cord_uid: zx78qhe5

nan

commend the authors for their excellent work. We wish to delve deeper into the debate surrounding the "obesity paradox" and discuss how one might reconcile this medical hypothesis with the extensive body of literature on atherosclerosis and cardiovascular disease.

First described in 2003, 2 the obesity paradox, or reverse epidemiology principal, states that there are better health outcomes for obese individuals than for normal weight matched individuals with certain medical conditions, such as diabetes, end-stage renal disease, hypertension, heart failure, coronary artery disease, and peripheral artery disease. There is even some evidence that higher BMI confers a positive survival value on sudden cardiac arrest, both out-of-hospital and in-hospital cardiac arrest with shockable rhythms (ventricular fibrillation and pulseless ventricular tachycardia), suggesting that the obesity paradox applies to the post-arrest population. 3 Since its inception, the obesity paradox has gendered hundreds of articles and studies on disparate clinical sub-populations.

The obesity paradox is an example of a statistical phenomenon known as bias resulting from observational studies. The mere association of two variables does not, in and of itself, demonstrate causality as the old adage, "correlation is not causation" states. This is particularly true for retrospective studies. Lack of statistical adjustment for cigarette smoking, for example, may lead to erroneous underestimation of the risk conferred by obesity in some early studies, 4 since smokers tend to have lower BMIs. The same logic holds true for nursing home residents, terminally ill, or cancer patients. It is necessary to account for individual disease severity and frailty. Use of the term "obesity", or use of BMI alone, is insufficient and may be misleading.

Obesity should be subdivided into categories: Class 1 (BMI of 30 to 34.9 kg*m -2 ), Class 2 (BMI of 35 to 39.9 kg*m -2 ), and Class 3 (BMI greater than 40 kg*m -2 ). Studies that cannot parse obese subjects into these categories should not assume sub-group homogeneity. Some studies which take a more rigorous view of this problem still appear to validate the obesity paradox. 3 This may be due to the varying levels of fitness of study subjects, a variable difficult to quantify posthoc. Outcome studies that take a rigorous look at the effect of BMI, 5 on the other hand, often do not support the obesity paradox. Perhaps we're looking at obesity the wrong way. Obesity is not a static variable, but consists rather of several different sub-populations. Obesity Class I subjects may frequently be otherwise healthy, with varying degrees of cardiovascular fitness, whereas obesity Class III subjects have higher participation of cardiovascular disease, metabolic syndrome and obstructive sleep apnea. Frequently used phenotypic indicators of the latter two of these conditions are abdominal circumference and waist-to-hip ratio. 6, 7 Central obesity correlates better than BMI as a measure of cardiovascular risk. 6, 7 The debate on obesity paradox is continuing, and moving into the sub-specialty realm. As anesthesiologists, we're struck that the wrong message is being given to the general public. The obesity paradox is a misnomer. 8 Obesity is not a benign condition, and obese individuals are not homogeneous; they are affected by their personal physical fitness and fragility -items all too often not included in the routine assessment tools. Nonetheless, obesity, particularly severe obesity, increases cardiovascular, diabetic, cancer, stroke risk, shortens life expectancy, and has been shown to be associated with worse COVID-19 outcomes. 9- 13 We believe that the obesity

Is the Obesity Paradox in Cardiac Surgery Really a Myth? Effect of Body Mass Index on Early and Late Clinical Outcomes

Reverse epidemiology of cardiovascular risk factors in maintenance dialysis patients

Effect of body mass index on survival after sudden cardiac arrest

Smoking and reverse causation create an obesity paradox in cardiovascular disease

Association of body mass index with clinical outcomes for inhospital cardiac arrest adult patients following extracorporeal cardiopulmonary resuscitation

Receiver-operating characteristic analyses of body mass index, waist circumference and waist-to-hip ratio for obesity: Screening in young adults in central south of China

Obesity and mortality: a review of the epidemiologic data. The American journal of clinical nutrition

Potential Pathophysiology of COVID-19 in Patients with Obesity

Overweight, obesity, and mortality in a large prospective cohort of persons 50 to 71 years old

The obesity epidemic, metabolic syndrome and future prevention strategies

paradox should be revealed for what it is: a statistical bias of a limited subset that is sometimes correct.