Like sarge said - its amazing if you just take the time to quantify your food intake just once & get a real idea of what you are really eating. Let me give you an obvious but very illustrative example. When I did my first competition I was 35 yrs old, had been lifting for nearly 20 yrs already but was sort of new at the diet thing. Actually at one point I was eating not enough. But I went from 16% to 8% bodyfat in about 3 months, dropped 18 lbs by strict diet manipulation and the addition of some cardio. I'd been using the same thermos for quite a while already so they didn't really make a difference in the big picture. Just gave me that kick in the pants, but it was all diet. I cut down not just to 'looking good' but fought my natural estrogen, 35 yrs of my body getting used to my particular lifestyle & diet, etc. strictly w/ detailed diet manipulation. BTW, this was a randomly tested show and I was part of the random testing - so completely natural.
Anyway - its the easy, no cost place to start. Eliminate anything in yoru diet and then you can start looking at different chemicals or whatever. But start w/ your diet in detail because its the foundation of everything your body does, its cheap, its easy and any tweaks can give immediate results.