CHICAGO, USA (Reuters) – people with a lower than normal weight is a risk of dying a 40 percent higher during the first month after surgery than patients with overweight, according to research released Monday.

The findings suggest that the rate of BMI, or BMI, may be useful to predict which patients suffer a greater risk as they recover from the operation, reported researchers American in Archives of Surgery.

Some previous studies that evaluated the role of BMI in the operation have had mixed results, said George Stukenborg, University of Virginia in Charlottesville, who participated in the study.

“Low BMI patients have increased risk of death 30 days after the operation,” said in an interview telephone Stukenborg

Researchers used data from nearly 190,000 patients who underwent a series of operations in 183 hospitals between 2005 and 2006.

The BMI is calculated by dividing weight in kilograms by height in meters squared. According to the Centers for Disease Control and prevention’s (CDC) of United States, people with a BMI of 18.5 to 24.9 have a normal weight; those with a BMI of 25 to 29.9 are overweight and who have a BMI of 30 or more is obese.

To search for a link between body weight and risk of death, classified patients into five groups: people with one BMI less than 23.1; people with a BMI of less than 26.3; 23.1 people with a BMI of 26.3 to less than 29.7; people with a BMI of 29.7 below 35.3; and people with a BMI of 35.3 or greater.

In total, 2.245 or 1.7 percent of the study participants were killed in the 30 days after the operation.

“We have found that patients in the lowest group had a probability of death 40% higher compared to the range medium,” said Stukenborg, referring to people in the category of overweight with a BMI of 26.3 to 29.7.

Even when the researchers adjusted by the type of operation and other risk factors, those with a BMI under still had one higher risk of dying during the first month after surgery compared with patients in an operation with greater weight.

Stukenborg said that it was not clear the why. The study did not follow recent weight loss, so it could be that people with a lower BMI were more sick from a beginning

Either way, Stukenborg said that doctors should consider the BMI when they plan operations for their patients.

Being overweight or being obese leads to many other risks, raising the chances of heart disease, diabetes, some types of cancer, arthritis and other conditions.

Diseases related to obesity correspond to almost 10 percent of the doctor in United States spending, or an average of 147,000 million (1008.900 million euros) a year.