Many people lose a ton of weight, some call it the "false body" - if one is a quick metabolizer, then fat will quickly drop off, as toxins are stored in the fat cells. Many will actually go underweight for a while and then start building back up.
If you are experiencing detox, the doctor can't help you and won't believe it's detox in most cases.
I highly suggest listening to this podcast with Tim Van Orden, there are 2 parts (scroll down to see):
http://rawfood.revvell.com/
He talks about his detox and how easy it is for him, now, to build muscle. He's on a simple raw diet and has been winning tons of races. He's ahead of younger runners eating the SAD.