Some of these replies show a complete lack of understanding of his injury. I have a vaguely similar problem that was keeping Gundogan out, so I've read quite a bit into his injury to try and find a solution to my own.
He put weight on because any sort of movement is painful. I hope the comparisons to Anderson were tongue in cheek, because they are totally different. It's not like a break for example, where you can still do certain exercises to stay in shape. From what I read, he was in pain through very little movement. He seems to have lost his weight and got back into shape very quickly.
Also as I understand it, his nerve inflammation issues look to have been sorted. I've not paid much attention to how he's getting on recently, but this is the furthest his recovery has got by a long way since the original injury.