Higher BMI Associated with Lower All-Cause Mortality

Adults that reported being overweight were associated with having lower odds of all-cause mortality compared with individuals having a lower body mass index (BMI), according to a study published in JAMA Network Open.¹ The study suggests that the common weight-loss recommendations aligning with normal BMI may need to be reevaluated.

Despite the current study only exploring older adults preparing for elective surgery, there have been significant reports on the link between BMI and mortality. And while a higher BMI has been found to increase various risks among patients, experts are still sifting through the proper evidence to support for patient recommendations.

“A high BMI (> 30 kilograms/meters²) increases the risk of death from heart disease, stroke, and some cancers; however, questions remain about the strength of the relationship between high BMI and all-cause mortality, and optimal BMI in relation to mortality,” according to the National Cancer Institute Division of Cancer Control & Population Sciences.² “These unanswered questions may be the result of methodological challenges related to population-based studies.”

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On top of the uncertainty behind BMI’s relationship with mortality, these associations also remain unclear within patients’ perioperative outcomes as well as the general patient outcomes among older adults.

Researchers conducted a cohort study of adults 65 and over undergoing surgery between February 2019 and January 2022. | image credit: fotoduets / stock.adobe.com

For many older patients, sarcopenia—or the tendency to lose muscle mass during aging—becomes an increasingly prominent issue related to BMI. While a high BMI can result in exacerbated outcomes among older adults, the loss of muscle mass can also be detrimental.³ With conflicting approaches to the optimal BMI for the best patient outcomes, researchers are working to better understand BMI’s relationship with various patient outcomes to improve recommendations and providers’ knowledge.

“Given that older adults experience unique age-related physiological changes which may modify the impact of BMI on health outcomes, questions remain about the appropriateness of current recommendations for overweight older adults to lose weight before surgery,” wrote authors of the current study.¹ “To test whether higher BMI is associated with better survival rates for older adults undergoing major elective surgery, we conducted a longitudinal cohort study of older adults undergoing major elective surgery at a large urban academic center.”

Possibly owing to the older adult populations’ gradually increasing need for greater body mass later in life, researchers hypothesized that a higher BMI would translate to lower odds of all-cause mortality following the older adult participants’ surgeries.

To test this hypothesis, researchers conducted a cohort study of adults 65 and over undergoing surgery between February 2019 and January 2022. With BMI as the primary study exposure, the researchers’ key study outcomes were patients’ 30-day and 1-year postoperative all-cause mortality. They also reported on any incidences of patient complications throughout their surgeries, including delirium, stroke, pulmonary issues, and more.

The final analysis included a total of 414 older adults (mean age, 75.9 years; 54.8% women) enrolled to undergo surgery. A total of 133 patients reported a BMI between 18.5 and 24.9, representing the largest portion of the cohort. Furthermore, 24.2% reported frailty, which is a notable factor among older adult patients’ BMI.

“Patients with a BMI of 25 to 29.9 had higher odds of survival at 30 days and 1 year following surgery compared with those with normal body weight,” wrote the authors.¹ “This BMI range was also associated with fewer overall postoperative complications, and these patients were more likely to be discharged [at] home.”

Confirming their hypothesis prior to the study, researchers found that underweight patients (BMI under 18.5) were associated with higher rates of 30-day and 1-year all-cause mortality. Moreover, patients with obesity had significantly lower mortality rates compared with patients of normal BMI, while patients with normal BMI also had lower mortality compared with underweight patients.

Finally, patients with higher BMIs also reported less perioperative complications than their counterparts with lower BMIs.

With confirmation of the researchers’ hypothesis, as well as further discrepancies regarding higher BMIs and how they translate to poorer or improved outcomes, results of this study highlight the need for more research into BMI guidelines, specifically among older adults.

“In this study, older adults with overweight or low-grade obesity who underwent elective surgery had higher odds of 30-day and 1-year mortality compared with those with a normal BMI,” they concluded.¹ “These findings challenge traditional preoperative guidelines emphasizing achievement of normal weight before surgery for older adults.”

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Reference

1. Canales C, Anderson M, Elashoff D, et al. Body mass index and postsurgical outcomes in older adults. JAMA Netw Open. 2025;8(8):e2528875. doi:10.1001/jamanetworkopen.2025.28875

2. Body mass index (BMI) and all-cause mortality pooling project. National Cancer Institute Division of Cancer Control & Population Sciences. March 14, 2025. Accessed August 29, 2025. https://epi.grants.cancer.gov/bmi-pooling-project/

3. Christmas C. Sarcopenia, body mass index and adults age 65-plus. Johns Hopkins Medicine. Accessed August 29, 2025. https://www.hopkinsmedicine.org/health/wellness-and-prevention/sarcopenia-bmi-older-adults