A big new discovery has extremely bad news for obese people, particularly those who are severely obese.

A new study found that people who are extremely obese are much more likely to have complications after heart bypass surgery than patients of a normal weight, according to an American Heart Association statement.

Severely obese people have much higher odds of developing an infection soon after heart byapss surgery, and they were more likely to stay longer at the hospital than patients with a normal weight.

The findings are based on an anlysis of data from 7,500 Canadians who had the operation between 2003 and 2014. In the surgery, blood flow is redirected around clogged arteries.

Those who have a body mass index above 40 are considered several obese. A normal BMI is 18.5 to 24.9.

Those who were extremely obese had triple the risk of infection after bypass surgery, and stayed a median of one day extra in the hospital. They were also 56 percent more likely to have complications within a month of surgery, with a risk of complications 35 percent higher.

“Based on the results of this study it appears that addressing infection risk might be an effective strategy to decrease the length-of-stay for patients with obesity who undergo coronary artery bypass surgery,” said Mary Forhan, Ph.D., the study’s senior author and assistant professor in the Department of Occupational Therapy, Faculty of Rehabilitation Medicine, at the University of Alberta in Edmonton, Canada, in the statement. “We know that wound healing in general is affected by poorly controlled glucose levels, and that adipose (fat) tissue may take longer to recover from trauma [such as the kind that occurs during surgery]. Therefore, as is recommended for all patients, efforts to ensure good glycemic control for patients with diabetes pre- and post-bypass are important.”