I've been doing this since last December (with a little break over Xmas and New Year cos I was on holday). I've dropped nearly 2 dress sizes.
You definitely get used to the fast days and stop thinking about food so much, and I think it also helps to re-educate you about what a portion is - yes you can be satisfied after a small chicken breast and salad/veg and no, you do not need that pudding!
I find it also works psychologically as you can think, I'll have that cake tomorrow, and then often you find you don't really want it.
I still train on fast days, but find hard swimming too difficult and tend to stick to short runs, cycling and weights type stuff. I think there are benefits to training without being fully fueled as it gets you used to not relying on sugar during training/races to get through. Also the endorphine rush from running when you haven't eaten much is immense!!
Dooze - good luck!