(Reuters Health) - People who get weight-loss surgery before they gain enough weight to become what’s known as “morbidly obese” are less likely to remain obese after the operation than heavier patients, a recent study suggests.

One year after bariatric surgery, only about one-third of patients lost enough weight to no longer qualify as obese, the study found. People who weren’t morbidly obese when they had surgery were over 12 times more likely to achieve this goal within a year, researchers report in JAMA Surgery.

“Our research suggests that waiting until a patient’s body mass index (BMI) is extremely high can hamper the benefits of undergoing bariatric surgery because these patients will have a lower likelihood of achieving the type of weight loss that leads to a healthy BMI,” said lead study author Dr. Oliver Varban, director of the Adult Bariatric Program at Michigan Medicine, the University of Michigan’s academic medical center in Ann Arbor.

“What we learned in this study is that patients and referring physicians should consider bariatric surgery as a primary therapy for obesity rather than the last resort,” Varban said by email.

Globally, 1.9 billion adults are overweight or obese, according to the World Health Organization. Obesity increases the risk of heart disease, diabetes, joint disorders and certain cancers.

Body mass Index (BMI) is a ratio of weight to height, and a way of estimating obesity. Having a BMI between 18.5 and 24.9 is considered a healthy weight, 25 to 29.9 is overweight, 30 or above is obese and 40 or higher is what’s known as morbidly obese.

An adult who is 5’ 9” tall and weighs from 125 to 168 pounds, for example, would have a healthy weight and a BMI of 18.5 to 24.9, according to the U.S. Centers for Disease Control and Prevention. An obese adult at that height would weigh at least 203 pounds and have a BMI of 30 or more.

Previous research has found obese people often struggle to shed excess pounds or keep weight off when they do lose it. Lifestyle changes such as following a healthy diet and getting regular exercise can often help in the short-term but fail to produce lasting results, particularly among people who have more than 100 pounds to lose before reaching a healthy weight.

Bariatric surgery has been shown to be the most effective treatment for morbid obesity, the study authors write.

Even though people with a BMI over 30 are considered obese, they may not get bariatric surgery until their BMI reaches 40 unless they have diabetes or other obesity-related health problems.

For the current study, researchers examined data on 27 320 adults who had weight-loss surgery in Michigan between June 2006 and May 2015.

On average, the patients had a BMI of 48 before their operation, and got down to 33 by the end of the first year.

Overall, just over 9,700 patients, or 36 percent, achieved a BMI under 30.

Only 8.5 percent of patients who had a BMI greater than 50 achieved a BMI of less than 30 after bariatric surgery, the study found. That compares to 31 percent of people who started out with a BMI of less than 40.

Patients who did manage to get their BMI below 30 had better odds of seeing improvements in obesity-related health problems, the study also found.

Compared to patients who remained obese a year after surgery, people who achieved a BMI of less than 30 were more likely to stop taking medications to control high blood pressure, elevated cholesterol and diabetes. They were also more likely to achieve remission of an obesity-related breathing disorder known as sleep apnea.

The study wasn’t a controlled experiment designed to prove whether or how having a lower BMI before surgery influences the odds of becoming non-obese afterwards.

Still, the findings suggest some obese people might not necessarily need to wait until they’re heavier to benefit from surgery, said Dr. Bruce Wolfe, author of an accompanying editorial and a bariatric surgery researcher at Oregon Health and Science University in Portland.

“These data demonstrate that this population with lower BMI appears every bit as likely to benefit from surgically induced weight loss than would be expected if they waited until they were more severely obese,” Wolfe said by email.

There are more people in the U.S. with a BMI between 30 and 35 than there are with BMIs above 35, Wolfe noted.

“Thus, a very large number of patients would possibly become surgical candidates,” Wolfe said.

SOURCE: bit.ly/2hqZuNx and bit.ly/2wpOKS5 JAMA Surgery, online July 26, 2017.