About 8 years ago I was in great shape - used to go the gym every other evening and do an hour on the cross-trainer; headphones on, head down and waddle away like a spastic.
I kept this up for months, and more importantly I kept eating the same stuff I normally ate; chocolate - a shit load, I love it. Crisps (chips to you yanks) by the bucket-full - love them. I figured I still had to have the things I enjoyed, just exercise and the weight will drop off. And it did - I looked the best I've ever looked. About a year later I met a girl, got comfortable and gave the gym up.
7 years later and I'm approaching 40, flabby, out of breath at the top of the stairs and shallow breathing as I'm not using my lungs for anything other than walking from my car to my desk. Feel like shit.
Well fuck that - 3 weeks ago I joined the local gym again and have started training again; couple of weights here and there but mainly back on the cross-trainer. Still eat the same shit I always have, but in 3 weeks I've lost 6lb (mostly probably water to start off with) but I feel better in myself for hauling my ass across the road to the gym.
The thing is to keep eating the same shit you normally do, don't deny yourself anything otherwise you'll go fucking mental.
Just exercise. That's it.
No diets, those things designed by people looking to cash in on people looking for an excuse not to exercise.
Don't want to be fat? Then get off your lazy ass and work off more calories than you eat, it's that fucking simple.