WASHINGTON — 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, which covers more than 334,000 adults who had emergency general surgery between 2019 and 2024.
The research will be presented at the American College of Surgeons (ACS) Clinical Congress 2026 in Washington, Sept. 26-29, where thousands of surgeons will convene to advance surgical quality, patient safety, and access to care.
“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, age 18 and older, in the U.S. who had emergency general surgery procedures between 2019 and 2024. ACS NSQIP is the leading 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 beginning in 2004.
The ACS NSQIP data allowed researchers to evaluate the relationship between BMI and level of frailty on outcomes including death, hospital length of stay, and readmission rates 30 days after initial admission, as well as the interaction between BMI and frailty and their combined associated risk on these outcomes. Frailty was assessed on a scale with values from one to five, with one indicating patients who had one comorbidity such as diabetes or chronic obstructive pulmonary disease and five 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% increased odds compared with normal-weight, non-frail patients. In contrast, obese patients 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% increased odds of death.
Compared to 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, 15.8% readmission rates, an average length of stay of 8.2 days, and an 88.5% discharge-to-home rate. For comparison, non-frail patients had a discharge to home rate of 96.9% and normal weight patients 90.3%.
Frailty reduced the protective effect of obesity on mortality. People who were both frail and obese faced 22% increased 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.”
Dr. 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.
Disclosures: Authors have no disclosures to report.
Citation: Cohn E, et al. The Synergistic Risk of Underweight Status and Frailty in Emergency General Surgery. Scientific Forum, American College of Surgeons (ACS) Clinical Congress 2026.
Note: Research abstracts presented at the ACS Clinical Congress Scientific Forum are reviewed and selected by a program committee but are not yet peer reviewed.
