Celebrity trainer Tony Horton says this is the one thing people trying to lose weight mess up

Tony Horton is one of the most visible people -- if not the most visible person -- in all of American fitness. The credit for that goes to his work creating P90X, the most successful home fitness program of all time. Perhaps the biggest reason that millions upon millions of people begin fitness programs is to lose weight. And of course most programs, including P90X, come with a comprehensive diet regimen to accompany the fitness portion. It was natural then, when we spoke to Tony recently, to as...