Study finds overweight older adults have lower postsurgical mortality than peers with normal BMI

Editor's Note

Older adults with a body mass index (BMI) in the overweight range had significantly lower odds of death after major elective surgery compared with those in the normal BMI category, an August 26 study published by JAMA Network reports.

The cohort study followed 414 adults aged 65 years and older evaluated at a preoperative clinic between 2019 and 2022. Overall 30-day mortality was 11%, but the risk varied sharply by BMI. Patients categorized as overweight (BMI 25.0–29.9) had the lowest mortality at 0.8%, compared with 18.8% among those with normal BMI (18.5–24.9). This translated into a markedly reduced odds ratio of 0.14 after adjustment for age, sex, frailty, and surgical risk. Obese patients (BMI 30.0–39.9) also had lower mortality compared with the normal group, while underweight patients (BMI <18.5) faced the highest risk, with 75% dying within 30 days.

At 1 year, survival trends were consistent: overweight and obese patients fared better than normal-weight peers, while underweight patients again had the poorest outcomes. A sensitivity analysis suggested the elevated risk was concentrated among those at the lower end of the normal BMI range (18.5–22.5).

The findings challenge current preoperative guidance that often emphasizes weight reduction to reach “normal” BMI before surgery. Researchers note aging alters body composition, fat distribution, and resilience to stress, which may shift the optimal BMI range for surgical outcomes. The protective effect of being overweight or mildly obese may reflect additional nutritional and metabolic reserves that help older adults withstand the physiological stress of surgery.

However, the benefits did not extend to patients with morbid obesity (BMI ≥40). This group experienced the highest rate of postoperative complications, with 79% having at least one event. Pulmonary complications, thromboembolic events, and strokes were more common, even though mortality rates were not as elevated as in the underweight group. Frail patients across all BMI categories also faced higher risks of death and complications.

The authors caution that BMI alone is a blunt measure that does not account for muscle mass, fat distribution, or undiagnosed illness that could influence outcomes. They recommend further multicenter studies to clarify how weight, nutrition, and frailty interact in surgical risk, and to inform whether weight loss should be encouraged in older patients preparing for surgery.