Good question, I'm answering this purely on what I have heard over the years, I really don't think there is much in the way of scientific fact to support any stance on this subject. First off it's not unhealthy to lose more than 2-3lbs per week which is what is recommended, if you are taking a multi vitamin, and have a well balanced meal plan. the main concern if you lose to much to fast is that you won't get the proper nutrition that your body needs, one of the trainers on biggest loser actually mentioned this to one of his trainees a couple weeks ago and some of them were losing 8 to 10 lbs on some weeks. Another thing that I have always felt is that if you are severly overweight it will not harm you to lose more than a couple pounds a week since we have so much to spare, but again you have to make sure your getting your vitamins, don't buy one of those over the counter one a day vitamins they are junk, buy one at a nutrition store that was made using "chelation" I think I spelled it right, anyway this is a process where they wrap the vitamin in an amino acid so you absorb more of it rather than your stomach just destroying most of it, hope that helps.
this bannana cracks me up.