A new study suggests that among people with type 2 diabetes, those who are overweight but not obese live longer than those at an average weight.

Pierluigi Costanzo and Stephen Atkin, doctors at the University of Hull, England, discovered that despite having a higher risk for developing strokes and heart attacks, overweight diabetics have longer lives than normal-weight patients with the same condition.

A person who is considered overweight has a body mass index (BMI) of 25 to 29.9. BMI is a metric value measuring body weight divided by height squared. So a man who is 5 feet 8 inches tall and 175 pounds would have a BMI of 26.61 and be considered overweight. If he took off 15 pounds, he would come into the normal weight zone with a BMI of 24.33. The formula is unable to differentiate between weight in fat and muscle — making it less of a tool for assessing individual fitness and more of a means for gauging obesity in populations. 

The researchers studied 10,568 patients diagnosed with type 2 diabetes over a decade.

According to their findings, diabetic patients who were underweight had a higher risk of dying during the course of the study. They registered a mortality rate three times greater than that of normal-weight patients.

Overweight patients, on the other hand, had a better chance of survival with 13 percent less likelihood of death, compared with both normal-weight and obese patients. The researchers call their discovery the "obesity paradox."

"These results are exploratory and hypothesis-generating," Costanzo said. "Living a healthy lifestyle aiming to achieve weight loss should be always pursued as already indicated by guidelines."

The doctors offered several possible reasons for the study's results.

The first is that the development of type 2 diabetes in obese people may significantly differ from patients who do not have this metabolic stress.

The second considers more external factors — type 2 diabetics with low BMI could possibly consume more alcohol and tobacco than others, which could also contribute to the development of their diabetes.

The third reason is that obese people are also more likely to be checked for diabetes than normal-weight patients, resulting in earlier diagnosis of their condition.

The researchers cautioned that the study's findings do not dictate an ideal BMI for patients. They still urge people with type 2 diabetes to adopt a healthier lifestyle.

This study was published in the journal Annals of Internal Medicine.

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