Try percentage body fat.

I was speaking with a personal trainer who said that people who have more muscle than fat are often in the obese range of the BMI.

A few years ago I went on weightwatchers, dropped from a size 16 to an 8, went to the gym 3-4 times a week. I only lost 2kg and got blasted by the group leader who accused me of not sticking to the diet. My trouble was I'd built muscle mass and had toned up. My body had changed but the scales did not reflect this.