Losing weight before bariatric surgery reduces risk of death by 40%

May 14 (UPI) -- Losing even a little weight before bariatric surgery can reduce the risk of complications from the procedure, a study published Thursday by JAMA Network Open found.

Compared to those who had a body mass index, or BMI, of 35 to 39.9 before the weight-loss procedure, people with BMIs of 40 and higher were up to five times more likely to die during the first 30 days after surgery, the authors observed.

Patients who were able to reduce their body weight by 10 percent or more before the operation reduced their risk of death by more than 40 percent, the authors said.

"Each year, hundreds of patients in the U.S. die after undergoing bariatric surgery," researchers from the University of Iowa, Wuhan University and Abbott Nutrition wrote in the study.

"Our study showed that preoperative weight loss, even at a moderate degree, was associated with lower risk of 30-day mortality," they wrote.

BMI is calculated by taking a person's weight in kilograms and dividing it by the square of their height in meters, according to the U.S. Centers for Disease Control and Prevention. It is a common measure of obesity, which affects more than 40 percent of American adults, according to agency estimates.

More than 250,000 weight-loss procedures are performed in the United States each year, according to the American Society for Metabolic and Bariatric Surgery. This includes surgeries in which the size of the stomach is reduced -- known as gastric bypass -- or a portion of the digestive tract is removed to change the way a person's body processes food.

Both are commonly used approaches to treat severe obesity.

In general, the risk of death in the first 30 days after the procedure is far less than 1 percent. However, surgeons have suggested that this risk may be reduced further if patients begin to lose weight before surgery.

Current surgery society guidelines don't recommend preoperative weight loss, due to a lack of evidence of its benefits, the authors of the JAMA Network Open analysis said.

For their study, researchers reviewed data on more than 480,000 bariatric procedures performed in the United States and Canada between 2015 and 2017. Nearly 80 percent of the patients were women -- with median age of 45 -- and just 511, or 0.1 percent, died within 30 days of surgery.

Compared with patients with a preoperative BMI of 35.0 to 39.9, patients with a preoperative BMI of 40.0 to 44.9 had a 37 percent higher risk for death during the first 30 days after surgery, the authors found.

Similarly, those with BMIs of 50 and above were more than twice as likely to die during the first 30 days following the procedure, the authors said.

In addition, compared to patients who did not lose any weight preoperatively, those who lost up to 5 percent of their body weight before surgery reduced their risk of death within 30 days by nearly 25 percent. Those who shed up to 9.9 percent of their weight reduced their risk by more than 30 percent.

Those who dropped more than 10 percent of their weight before surgery reduced their risk of death within 30 days by more than 40 percent.

The authors suggested the reasons for this reduced risk might be that weight loss lowers patients' chances of developing complications like venous thromboembolism, including deep vein thrombosis, as well as apneic episodes -- or breathing problems -- during and after surgery.

The weight loss also might lessen the complexity of the surgery, further reducing risk for complications, the authors said.

"Although current clinical guidelines do not require preoperative weight loss, and a decision to perform bariatric surgery should not be based on whether and how much preoperative weight loss is achieved, it may be beneficial for patients with obesity to be referred to an established weight loss program before surgery to reduce the risk of mortality," the authors wrote.