Amit, I think you are doing very well in the right way, congratulations!

As for bone density loss, osteoporosis, BMI and dieting, here is a webmd article discussing just that:

http://www.m.webmd.com/a-to-z-guides...et-weight-loss

Basically, do not diet too fast - keep calories above 1,200 per week - and maintain your BMI in the 'Healthy' range. Too low, and bone loss can occur over time. Obviously, this is all dependent on sticking to a balanced diet with all the necessary vitamins and minerals, or supplements.

Dave.