People with obesity may initially shed more excess pounds with an older operation known as Roux-en-Y gastric bypass than with a newer sleeve gastrectomy procedure, but a research review suggests that longer-term, which one is better for weight loss remains unknown.

Researchers examined data from previous studies on a total of 2,475 obese patients in 13 countries who had weight-loss surgery between 2006 and 2018. One year after surgery, Roux-en-Y resulted in greater weight loss than sleeve gastrectomy, and this trend persisted three years after the procedure.

But five years after surgery, there was not enough evidence to determine whether one procedure might be better than the other, researchers conclude in the Annals of Surgery.

“There are insufficient data from RCTs to draw any conclusions regarding the long-term comparative effectiveness,” lead study author Yung Lee of McMaster University in Hamilton, Ontario, and colleagues write.

Surgical weight loss has gained traction in recent years as a growing number of extremely obese patients turn to this option after failing to lose weight through diet, exercise, or medication. Like all surgery, it isn’t risk-free, and bariatric operations in particular carry a risk of malnutrition.

With a sleeve gastrectomy, surgeons divide and remove around 80% of the stomach using special surgical staplers, which leaves the stomach looking like a long thin banana.

For a Roux-en-Y gastric bypass operation, the same surgical staplers are used to divide the stomach to create a small pouch about the size of an egg. Surgeons then create a connection between the pouch and the small intestine so that food travels directly into the end of the small intestine, bypassing the stomach and the first portion of the small intestine.

Researchers focused on changes in patients’ body mass index (BMI), a measure of weight relative to height. A BMI between 18.5 and 24.9 is considered a healthy weight, while 25 to 29.9 is overweight, 30 or above is obese, and 40 or higher is what’s known as severely or morbidly obese.

All of the patients in the analysis were considered good candidates for weight-loss surgery under current treatment guidelines because they were severely obese people with a BMI over 40 or obese individuals with a BMI over 35 who had obesity-related chronic health problems.

One year after surgery, patients who had Roux-en-Y procedures had an average BMI reduction of 1.25 points more than with sleeve gastrectomy, the study found. More Roux-en-Y patients had high cholesterol return to normal levels within a year of surgery than with sleeve gastrectomy, the study also found.

There was no meaningful difference between surgeries in the proportion of patients who achieved remission of conditions like diabetes and high blood pressure. Rates of minor and more serious complications were also similar.

One limitation of the analysis is that few of the smaller included studies reported on five-year outcomes, the researchers note.

Another drawback is that BMI is no longer considered the ideal way to assess the effectiveness of weight-loss interventions, the study team points out.