This is a couple of years old, but it's very interesting:
http://www.time.com/time/health/arti...4857-1,00.html
Two salient points I got from this article:
1) Exercising makes us hungrier, making it more difficult to make healthier food choices and/or eat sensible portions. This might seem easy to overcome if you calorie count (as I do), but I know that if I'm physically hungry, I more easily give in to temptation.
2) Formal exercising tires us, and we may compensate by doing less activity throughout the day that we normally would have. I can bear witness to the truth of this. Many a time when I used to do a bootcamp class at the local gym, I would come home wiped out and plop on the couch. Even though there was always housework to do, I would make one excuse after another for putting it off until "tomorrow."
Now, some might find the article discouraging, but I had the opposite reaction. For years, I would start a diet AND exercise program (because the two always went hand in hand) and be gung ho about it for a while. Then, eventually, all the energy required to keep up with it all would discourage me. The exercise would become drudgery, a chore, no matter what I did---treadmill, elliptical, bootcamp classes, spinning, etc. Then, I would just give up on it all---including the eating habits.
I think because exercise has been marketed right along with diets, it was ingrained in my mind that one was irrevocably linked to the other. I never imagined until the last couple of years [when these studies started appearing about exercise's negligible effects on weight loss] that I could lose weight without busting my butt doing formal exercise. It is such a relief to me to know that I can. Now I'm more focused on working activity into my everyday routine rather than having to set aside 1 - 2 hours, 5 - 6 days a week for formal exercise. Obviously, I care about my health and exercise helps with that, so I'm conscious of moving more---I have my treadmill set up so that I work on the computer while walking (2.5 mph, 5 elevation), I bike to the library when the weather permits, I park my car in the farthest parking spot from where I shop, etc.
The one exception I make to all this is strength training. That type of exercise can actually change your shape, so I believe in it. I've seen it firsthand with my sister. She is about 180, but she looks MUCH smaller than that and is tight and toned because she has regularly done strength training for at least three years now.