Weight Loss Before Bariatric Surgery Reduces Mortality Risk

Yangbo Sun, MD, PhD

Weight loss before bariatric surgery was associated with a lower risk of 30-day mortality, study investigators found.

The findings from Yangbo Sun, MD, PhD, and a team of investigators could help inform future updates of clinical guidelines regarding bariatric surgery.

Sun, from the epidemiology department at the University of Iowa College of Public Health, and colleagues used data from 480,075 patients who underwent bariatric surgery from 2015-2017 in the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program. The data covered >90% of all bariatric surgery programs in the US and Canada.

The team extracted preoperative and demographic variables, comorbidities, information on the procedure, and 30-day outcomes. Patients were excluded if their highest recorded preoperative body mass index (BMI) was <35 or if they gained weight before surgery.

At the bariatric center, the patient had their highest preoperative weight recorded within 1 year before the principal operation. The weight closest to the day of surgery was considered the most recent weight documented in the medical record within 30 days before the operation or at the time the patient was considered a surgery candidate. The investigators also recorded the patient’s most recent height within 30 days before the operation.

Sun and colleagues defined weight loss as the difference between the highest recorded preoperative weight and preoperative weight recorded closest to the procedure. BMI reduction was considered the difference between the highest recorded BMI and BMI closest to the day of the operation.

The primary outcome was death within 30 days of bariatric surgery. The team obtained the information from the reporting of mortality up to and including day 30 after the operation.

Of the more than 480,000 patients who received bariatric surgery, 79.8% were women and the mean age was 45.1 years old (range, 18-80 years old). There were 511 (.1%) deaths during the operation or within 30 days after the surgery.

The mean percentage of reduction in body weight before surgery was 4% (range, 0-70.2). Patients with greater weight loss (>10%) before bariatric surgery were slightly older (mean age, 47.1 years old vs 44.7 years old; P <.001), more likely to be male (25.4% vs 18%; P <.001), and non-Hispanic white (70.6% vs 54.6%; P <.001) compared to patients without weight loss before surgery.

Among those who with greater weight loss, they were more likely to undergo Roux-en-Y gastric bypass compared to those without weight loss (30.1% vs 22%; P <.001). Similarly, those with greater weight loss had higher highest recorded preoperative BMI (51 vs 45.9; P <.001) and lower preoperative BMI closest to the day of surgery (43.4 vs 45.9; P <.001) compared to those without weight loss.

Compared to those with a preoperative BMI of 35-39.9, the adjusted odds ratios for 30-day mortality for patients with a preoperative BMI of 40-44.9 was 1.37 (95% CI, 1.02-1.83), 2.19 (95% CI, 1.64-2.92) for a BMI of 45-49.9, 2.61 (95% CI, 1.9-3.58) for a BMI 50-54.9, and 5.03 (95% CI, 3.78-6.68) for a BMI >55 (P <.001 for all).

What’s more, compared to no weight loss, the adjusted odds ratios for 30-day mortality for those with weight loss of more than 0-<5% was .76 (95% CI, .6-.96), .69 (95% CI, .53-.9) for 5-9.9%, and .58 (95% CI, .41-.82) for >10% (P=.003 for all).

Overall, higher preoperative BMI was associated with a higher risk of 30-day mortality following bariatric surgery. Even slight weight loss was linked with significantly lower risk of 30day mortality.

The study has clinical importance because hundreds of patients die after undergoing bariatric surgery each year. It could be beneficial for patients with obesity to be referred to an established weight loss program before surgery to reduce the risk of mortality.

The study, “Association of Preoperative Body Weight and Weight Loss With Risk of Death After Bariatric Surgery,” was published online in JAMA Network Open.