In fact, according to recent research out of Canada, underweight people have an even higher risk of dying than obese people do. The researchers analyzed51 studies and found that underweight people were 1.8 times as likely to die for any reason than people with normal BMIs, while obese people were 1.2 times as likely. The researchers point out that BMI can be used to determine whether someone is carrying too much fat as well as whether a person has enough bone and muscle mass to be healthy.

MORE: Take the Body Health Quiz to Find Your BMI