The obesity paradox: body mass index and outcomes in patients undergoing nonbariatric general surgery

Ann Surg. 2009 Jul;250(1):166-72. doi: 10.1097/SLA.0b013e3181ad8935.


Objective: We sought to examine the effect of body mass index (BMI) on 30-day morbidity and mortality in a large cohort of patients undergoing nonbariatric general surgery.

Summary background data: Obesity has long been considered a risk factor for poor outcomes from a variety of surgical procedures, yet recent studies of critically and chronically ill patients suggest that overweight and obese patients may paradoxically have better outcomes than "normal" weight patients.

Methods: A prospective, multi-institutional, risk-adjusted cohort study of 118,707 patients undergoing nonbariatric general surgery who were included in the National Surgical Quality Improvement Program Participant Use database in 2005 and 2006 was performed. Outcomes and risk variables were compared across NIH-defined BMI class using analysis of variance, Bonferroni multiple comparisons of means tests, and multivariable logistic regression.

Results: After adjusting for all significant perioperative risk factors, the risk of death according to BMI exhibited a reverse J-shaped relationship, with the highest rates in the underweight and morbidly obese extremes and the lowest rates in the overweight and moderately obese. Overweight (odds ratio, 0.85; 95% CI, 0.75-0.99) and moderately obese (odds ratio, 0.73; 95% CI, 0.57-0.94) patients had a significantly lower risk of death than normal weight patients. There was a progressive increase in the likelihood of a complication with increasing BMI class, almost entirely due to increasing rates of wound infection.

Conclusions: Overweight and moderately obese patients undergoing nonbariatric general surgery have paradoxically "lower" crude and adjusted risks of mortality compared with patients at a "normal" weight. This finding is in contrast to observations from the general population, confirming the existence of an "obesity paradox" in this patient population.

Publication types

  • Multicenter Study

MeSH terms

  • Body Mass Index*
  • Chronic Disease / epidemiology
  • Cohort Studies
  • Critical Illness / epidemiology
  • Female
  • Humans
  • Male
  • Middle Aged
  • Obesity / epidemiology*
  • Obesity / mortality
  • Obesity / surgery*
  • Obesity, Morbid / epidemiology
  • Obesity, Morbid / mortality
  • Overweight / epidemiology
  • Prospective Studies
  • Risk Factors
  • Surgical Procedures, Operative / mortality
  • Surgical Procedures, Operative / statistics & numerical data*
  • Thinness / epidemiology
  • Thinness / mortality
  • Treatment Outcome
  • United States / epidemiology