When I first started working more with people who wanted to lose weight I found myself to be very frustrated. More often than not, the results weren't happening. I'd generally expect them to lose 1 to 1.5 pounds per week and at the end of 4 weeks, many of them were coming back losing none, and many times gaining a small amount!
I've heard the cliches of "you can't out train a bad diet," or "weight loss is 80% nutrition and 20% exercise," "abs are made in the kitchen ." Though diet may not be the deciding factor in every situation, for the majority of people trying to improve body composition, it is.
No matter how hard you train, no matter how consistent you are, even the best exercise program alone will not get you the results you want.
Combining both commitments to training and nutrition will give you 3-5x the rate of fat loss as training alone. And by this commitment, I don't mean starving yourself to death or going on an intense calorie restricted diet. Look at this article to see how this could even possibly damage your metabolism.
There is no doubt that committing to a training program will bring you many physiological benefits especially in the short term. But until you make the change in your diet, losing weight will be walking up a never-ending hill, a lot of sweat and hard work without getting where you want to go.
Most of you know this. But I'm going to repeat it. If you really want to lose weight, quit justifying how hard you are working in the gym. Heck, maybe you even need to stay out of the gym and simply walk every day and focus on your diet. Whatever the case, in whatever combination you need, it takes both. But a little more work on the diet will go a long way.