For weight loss it doesn't matter what you eat as long as you create a calorie deficit. I've lived this truth many times. That said, healthy foods with lots of bulk and fibre tend to fill you up a lot more than calorie-dense fast foods, so most people find it EASIER (and that's the whole idea, right?) to stick to a weight loss program that revolves mainly around nutritious fare. For me, the 80/20 rule works just fine: about 80% healthy and 20% whatever. (My whatever doesn't include fast foods, because I don't enjoy them. I lean more toward indulgences like fresh baguette and Brie cheese, crepes with Nutella, etc.)
There is no way to "spot reduce" your fat. Your body will drop its fat in a sequence that's unique to you and cannot be altered. If you tend to gain most of your weight in the hips, that's where you'll drop it first, no matter what exercise you do. The only thing abdominal exercises will do is tone up the muscles underneath the fat. These muscles will likely become visible only after you've reached your goal weight.