Last updated: May 13, 2016

According to current guidelines, people who have a body mass index (BMI) over 25 are classified as "overweight"—which is not considered to be a good thing for your health. But new research suggests it may not be quite as bad as experts thought. 

The surprising study, published Wednesday in JAMA, found that people who are a bit heavier are the least likely to die young. Using data from three different periods—1976 to 1978, 1991 to 1994, and 2003 to 2013—Danish researchers examined the link between BMI and mortality in more than 120,000 people.

The discovered that in the first group, folks with a BMI of 23.7 (in the "healthy" range) had the lowest risk of death. In the second cohort, the mortality rate was lowest for people with a BMI of 24.6 (which is at the high end of the healthy range). But in the most recent group, those with a BMI of 27 (roughly in the middle of the overweight range) had the lowest risk of dying from any cause.

“Compared to the 1970’s, today’s overweight individuals have lower mortality than so-called normal-weight individuals,” explains the study's senior author, Børge G. Nordestgaard, MD, a clinical professor at the University of Copenhagen. But why remains a mystery, he says. “The reason for this change is unknown."

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Nonetheless, Dr. Nordestgaard cautions people not to get the wrong idea from his research:  “Our results should not be interpreted as suggesting that now people can eat as much as they like, or that so-called normal weight individuals should eat more to become overweight,” says Dr. Nordestgaard. “That said, maybe overweight people need not be quite as worried about their weight as before.”