A new HealthPartners study is helping to address a quandary for doctors treating obesity and diabetes — when to turn patients to bariatric weight-loss surgery and when to keep them focused on diet, exercise and medication.

Comparing a population of young, obese patients with type 2 diabetes, the researchers found a 49 percent reduction in microvascular problems — which can lead to kidney failure, blindness and amputations — among those who underwent surgery vs. those who didn’t.

“We were surprised at the magnitude of the benefit,” said Dr. Patrick O’Connor, a researcher with the HealthPartners Institute. “A 49 percent reduction ... is a big deal.”

Bloomington-based HealthPartners’ health plan contributed anonymous patient data for the study along with Kaiser Permanente health plans in California and Washington. Only patients with type 2 diabetes and severe obesity (100 pounds or more over healthy weights) were included.

Because the study retrospectively looked at the results of surgeries, which took place from 2005 to 2011, the researchers had little control over the demographics of their study subjects. What they found is that the 4,024 patients who chose surgery were younger than most people with diabetes, and also had lower rates of cardiac problems and insulin drug usage. Most were female. Researchers then created a comparison population of 11,059 patients with diabetes and obesity who didn’t undergo surgery.

Medical records only showed their health through 2015, which would have been too soon to determine whether surgery prevented more complications such as blindness that occur over time. But the researchers could check for microvascular problems — blockages of the small arteries that feed blood to the eyes, kidneys and nerves — that lead to complications.

Other studies have shown that patients after surgery see remissions in their diabetes, because their blood sugar levels stabilize. But that information isn’t always persuasive.

“To many people with diabetes, their blood sugar levels feel like an abstract concept,” said Dr. Rebecca O’Brien, an Oakland, Calif., researcher who led the study. “What matters more to them is avoiding the harmful complications.”

Many factors influence whether to pursue bariatric surgery, including patients’ mental health and ability to adhere to post-surgery diets.

O’Connor said the research argues for discussing surgery with any younger patients with severe obesity and diabetes. The study data is being fed into a decision-support computer system that will alert doctors when their patients are good surgery candidates.