I've lost about 3 stone in the last 3 months so maybe I can offer some advice...it may not be medically sound/correct but I tried diets and things and in the end I just took matters into my own hands!
Firstly I started exercising, I have a punchbag which I kick the sh*t out of at every given opportunity...I also started lifting weights, nothing huge, just dumbells. I changed my diet drastically...LOADS of water, cereal for breakfast, some fruit and the evening meal would consist of a lump of protein (lean steak or chicken) and loads of vegetables (usually brocolli) I completely cut out chocolate, fizzy drinks, crisps...all junk food!
Although this new lifestyle made me feel good inside and made me feel superior to all the people who still eat crap...I wasn't losing much weight! The weightloss started to happen when I started to get a bit depressed about my girlfriend and the prospect of us not being together (that's a different thread) I pretty much stopped eating, just drinking water and whoosh! The weight dropped off! My stomach shrunk and now it takes a lot less food to fill me right up...and that is useful!
The girlfriend situation is more positive now, I've started eating again but still only really eat once a day. The way I lost weight is not correct by any means and doctors would probably have a right go at me BUT it taught me a few important things.
1: Drink water! A lot of people mistake thirst for hunger.
2: Eat less...a LOT less! The average portion size these days is HUGE!
3: Stop eating when you are no longer hungry! Listen to what your body is telling you!
4: Do all of the above and remain active and the weight will drop off!