What a prick , honestly , calling me very religious just because I have an opinion you don ' t agree with ! WHOA ! <| sep |> Nah , bmi is a load of crap . Two people with the same height and weight will have the same bmi , even if one person is a 5 % body fat marathoner and the other is morbidly obese . The real issue here is your parents ' method of motivation . Unfortunately , you ' re at an age where it ' s easy for them to ignore you , and hard for you to change their minds . Not impossible , just difficult . Motivation is a tricky business . Far too often , people will commit to either positive or negative reinforcement , and abandon the other entirely . From various experiments , it seems like a ratio of 6 positive comments for every 1 negative comment works the best . No idea how you can convince them to try it though .