My wife and I decided to go on a diet recently (3 weeks ago) we've completely changed our eating habits and bought exercise machines and weights which we use every night. During the 3 weeks my wife has gone from 17.2 stone to 16.1 and my weight has gone from 22.10 to 20.00 However I have read on many forums that loosing weight too fast is bad for you. Can anyone explain why this is. The only explanation I can find online is you loose muscle however my chest, arm and leg muscles seem to be growing now wasting away. I use the cross trainer every night for 45 minutes and do weights every 2nd night for around 30 minutes. My wife uses the cross trainer every night for 30 minutes and an arobic exercise every night for 30 minutes.