Many severely obese patients have less pain and better mobility in the first few years after weight loss surgery, a U.S. study suggests.

Researchers followed more than 2,200 obese patients who had weight loss surgery. After one year, 58 percent of them reported less pain and 77 percent said they had better physical function.

By three years, the proportion of patients still reporting improvements in pain and physical function dropped significantly to 49 percent and 70 percent, respectively.

Patients did, however, report consistent improvements in walking ability at one and three years, and those who started with knee and hip problems also reported lasting pain reductions and mobility increases around these joints.

While surgery remains more effective for lasting weight loss than alternatives such as dieting and exercising, the findings suggest that not all surgical patients will get the same results, said lead study author Wendy King, a public health researcher at the University of Pittsburgh.

The amount of weight lost after the surgery, rather than the type of surgery, was "consistently related to improvements in pain and function," King 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.

Surgical weight loss has gained traction in recent years, but it is not risk-free. For example, patients can become malnourished.

In the U.S. alone, roughly 180,000 people get these procedures each year, according to the American Society for Metabolic and Bariatric Surgery (ASMBS).

The most common operation, known as a sleeve gastrectomy, reduces the stomach to the size of a banana. The next most common, known as Roux-en-Y, creates an even smaller stomach pouch.

King and colleagues focused on people who had Roux-en-Y operations or procedures known as laparoscopic adjustable gastric banding, which also reduce the stomach size but can later be reversed.

Most patients were women, and half were at least 47 years old at the start of the study. They were all severely obese.

Overall, reductions in weight and depressive symptoms were associated with more improvements in pain and mobility, researchers report in JAMA.

Younger patients, men, wealthier and less obese people were also more likely to have improvements in pain and mobility at one and three years after surgery.

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The study was observational, and it can't prove weight loss surgery directly causes reductions in pain or increases in mobility, the authors note.

Another limitation of the study is the lack of a control group of people who lost weight without surgery, making it impossible to say whether the operations might lead to better or worse results than losing weight through alternative methods such as diet or exercise, the researchers also point out.

It's also possible that obese patients would need more than just surgical weight loss to achieve the best outcomes in pain and physical function, said Dr. John Morton, chief of bariatric and minimally invasive surgery at Stanford School of Medicine.

"Clearly patients who have obesity and joint disease are patients with chronic disease," Morton, also immediate past president of ASMBS, said by email.

"These patients likely need to have follow up and access to care for needed services like physical therapy," added Morton, who wasn't involved in the study.

While it's possible patients might achieve reductions in pain and improved mobility if they lost enough weight through diet and exercise, this often doesn't happen, noted King.

"Unfortunately, lifestyle interventions that focus on dietary intake, eating behaviors, exercise, physical activity level, or a combination of these factors have not been able to achieve a comparable magnitude of weight loss" as surgery, King said.