My sister is under the care of a nutritionist due to some health issues. At her first appointment he put her on his funky scales that say fat content, muscle weight, bone weight etc and came out with something quite shocking. Her bones alone weighed something like 45kg and for her height to have the right BMI she is supposed to be 55kg total. Now considering she has all of her organs as well as water & fat to add to her 45kg of bones, there is no way she could be 55kg and be healthy. BMI just doesn't work for everyone.