Underweight patients face 92% higher odds of death after emergency general surgery

by American College of Surgeons

edited by Sadie Harley, reviewed by Robert Egan

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Underweight patients are more likely to die after emergency general surgery than patients who are normal weight or overweight, and patients who are both frail and underweight face an even higher risk of death and other adverse clinical outcomes, according to new research findings.

The study drew on the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) database and included more than 334,000 adults who had emergency general surgery between 2019 and 2024.

The research was presented at the American College of Surgeons (ACS) Clinical Congress 2026 in Washington, Sept. 26–29.

"Our study shows that patients who are both underweight and frail have the worst outcomes. We also saw that frailty reduces the positive impact of the obesity paradox—the finding that patients who are overweight, but not at the extremes of obesity, tend to have better outcomes. That protective effect is lost if a patient is frail," said lead study author Ellen Cohn, MD, MPH, a third-year general surgery resident at the University of Chicago.

"What we take away from this study is that risk can be mitigated. We can make real-world changes to body mass index (BMI), and physical therapy can reduce frailty. What is unique about our study is that we were able to look at the impact of BMI and frailty together," she said.

Using the ACS NSQIP database, researchers identified all adults ages 18 and older in the U.S. who had emergency general surgery procedures between 2019 and 2024.

ACS NSQIP is a nationally validated, risk-adjusted, outcomes-based program to measure and improve the quality of surgical care in hospitals. More than 600 hospitals participate in the ACS NSQIP adult program, which began enrolling private-sector hospitals in 2004.

The ACS NSQIP data allowed researchers to evaluate how BMI and frailty were associated with death, length of hospital stay and readmission within 30 days of initial admission.

Researchers also assessed the combined risk associated with BMI and frailty. Frailty was assessed on a scale from 1 to 5, with 1 indicating patients who had one comorbidity, such as diabetes or chronic obstructive pulmonary disease, and 5 indicating patients who had five diseases and were severely frail.

Study results

• Among 334,278 patients included in the analysis, 37.6% were frail—more than one in three.

• After adjusting for clinical factors, underweight patients had the highest risk of death, with 92% higher odds than normal-weight, nonfrail patients. In contrast, patients with obesity had lower odds of death than normal-weight patients: 43% lower at a BMI of 30.0–34.9 and 27% lower at 35.0–39.9. At a BMI of 40 or higher, there was no significant difference.

• Frailty alone was associated with 59% higher odds of death.

• Compared with patients who were normal weight and not frail, those who were both underweight and frail had the worst outcomes across all measures: 9.8% mortality, a 15.8% readmission rate, an average length of stay of 8.2 days and an 88.5% discharge-to-home rate. For comparison, nonfrail patients had a discharge-to-home rate of 96.9%, and normal-weight patients had a rate of 90.3%.

• Frailty reduced the protective effect of obesity on mortality. People who were both frail and obese faced 22% higher odds of death, whereas those who were obese but not frail remained 7% less likely to die after emergency general surgery.

"While the focus of our study was on underweight and frail patients, we were surprised to find that obese patients did better," said study co-author Justin S. Hatchimonji, MD, assistant professor of surgery in the section of trauma and acute care surgery at the University of Chicago.

"I think recognizing the importance of not only underweight status, but also frailty, helps emergency general surgeons plan for postoperative outcomes and think about how to best manage these patients over the long term."

Cohn said the findings can be used to improve postoperative outcomes regardless of frailty scores.

"Thinking about older patients, it's important to focus on what we can affect: nutrition, making sure protein goals are met, bone health and vitamins," she said. "Keeping patients healthy that way can have a bigger impact on outcomes than the other comorbidities that make up the frailty score. We know that you can change underweight status and as a result get a better outcome."

A limitation of the study is that a large database study cannot prove cause and effect, only an association.

Co-authors are Hans Strobl, MD; Phillip Dowzicky, MD, FACS; Abid D. Khan, MD, FACS; and Diane N. Haddad, MD.

More information

Cohn E, et al. The Synergistic Risk of Underweight Status and Frailty in Emergency General Surgery.

Key medical concepts

UnderweightFrailtyMortalityObesity

Clinical categories

General surgeryWeight managementHealthy aging Provided by American College of Surgeons Who's behind this story?

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