Here are the best start points for two weeks on the Camino. Most of these starts allow you to finish in Santiago.
I lost about 8kgs, about 18 lbs, over a four week period. So yes I did lose a lot of weight on the Camino.
However, losing weight was never one of my reasons for walking. I did not set out on the Camino to lose weight and I must admit that it never entered into my mind at any time while I was there.