Even moderate weight loss before bariatric surgery significantly reduces the risk for mortality in the 30 days after the operation, according to study results published in JAMA Network Open.

Bariatric surgery is the most effective and durable treatment for clinically morbid obesity, but this voluntary procedure has a nonzero risk for mortality that the patient would otherwise not experience. Although weight loss before bariatric surgery is sometimes recommended by physicians and health insurance payers, current clinical guidelines do not recommend preoperative weight loss given the lack of consistent findings on its association with postoperative weight loss and risk for mortality.

To examine the association of preoperative body mass index (BMI) and weight loss within 1 year prior to bariatric surgery with postoperative risk for mortality, data from 480,075 patients who underwent bariatric surgery between 2015 and 2017 were analyzed. The average age of patients was 45.1±12.0 years and the majority (79.8%) were women. Patients with a highest recorded preoperative BMI of <35.0 kg/m2 and those who gained weight before surgery were excluded.

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The mean percentage of reduction in body weight before surgery was 4.0% (range, 0%-70.2%). Patients with greater preoperative weight loss (≥10.0%) were older (47.1±11.9 vs 44.7±11.9 years; P <.001) and more likely to be male (P <.001) and non-Hispanic white (P <.001) compared with patients with no preoperative weight loss. Patients with greater preoperative weight loss also had a higher average highest recorded preoperative BMI (51.0±10.3 vs 45.9±7.9 kg/m2; P <.001) and a lower preoperative BMI closest to the day of the surgery (43.4±8.7 vs 45.9 kg/m2; P <.001), were less likely to have smoked tobacco in the year prior to surgery (P <.001), and were more likely to have had ≥2 comorbid conditions at baseline (P <.001) and to have undergone Roux-en-Y gastric bypass surgery (30.1% vs 22.0%; P <.001) compared with those with no preoperative weight loss.

A total of 511 deaths (0.1%) occurred during or within 30 days after the procedure. After adjusting for a variety of potential confounders, a greater preoperative BMI was significantly associated with a greater risk for 30-day mortality. A preoperative BMI ≥55.0 kg/m2 had a multivariable-adjusted odds ratio (aOR) for 30-day mortality of 5.03 (95% CI, 3.78-6.68), and the aOR was 2.61 (95% CI, 1.90-3.58) for a BMI of 50.0 to 54.9 kg/m2, 2.19 (95% CI, 1.64-2.92) for a BMI of 45.0 to 49.9 kg/m2, and 1.37 (95% CI, 1.02-1.83) for a BMI of 40.0 to 44.9 kg/m2 compared with a preoperative BMI of 35.0 to 39.9 kg/m2 (P <.001 for trend). In a similar fashion, a higher peak recorded preoperative BMI was significantly associated with a greater risk for 30-day mortality (P <.001 for trend).

Greater weight loss before surgery was significantly associated with a decreased risk for 30-day mortality. A preoperative weight loss of ≥10.0% had an aOR for 30-day mortality of 0.58 (95% CI, 0.41-0.82), with the aOR for a 5.0% to 9.9% weight loss being 0.69 (95% CI, 0.53-0.90) and the aOR for a weight loss >0% and <5% being 0.76 (95% CI, 0.60-0.96) compared with no preoperative weight loss (P =.003 for trend).

Taken together, these findings indicated that a higher preoperative BMI was significantly associated with a higher risk for 30-day mortality after bariatric surgery and that even a moderate weight loss of >0% to <5% was associated with a significant decrease in this risk.

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This study’s strengths included its large and diverse sample of patients, robust information regarding potential confounders, and significant, actionable findings. A limitation to this study was the inability to establish causality; however, mortality rate among patients who undergo bariatric surgery is too low to reasonably conduct a conclusive randomized clinical trial.

Future studies should investigate programs for or motivations behind preoperative weight loss and should examine the longer-term effects of preoperative weight loss on risk for mortality.


Sun Y, Liu B, Smith JK, et al. Association of preoperative body weight and weight loss with risk of death after bariatric surgery. JAMA Netw Open. 2020;3(5):e204803.

This article originally appeared on Endocrinology Advisor