How old are you? Are you sure that's your real age?
Doctors say that answer can depend, in large part, on your weight. "Biggest Loser" doctor, Robert Huizenga and author of "Where Did all the Fat Go," teaches contestants how fat is cutting their lives short. He takes into account weight, fitness level, diseases and family medical history.
San Diego-based "Real Age" also uses a complicated formula, based on thousands of scientific studies, that helps people assess their biological age online. They say your waistline measurement should be less than half your height. Otherwise, fat there can start to make you physically really old.
"And it can both crush, push out, distort and infiltrate your vital organs and it does all kinds of health damage," said Val Weaver, Real Age Editor in Chief.
The test is available online -- visit Real Age.com to take the test.