The latter pretty much proves the point, doesn't it? Diets work. Eat less, exercise more, and you lose weight. Maybe not as much as you want to, as fast as you want to, but it does eventually work. Create a calorie deficit, and your body mass goes down. Which seems to imply that the problem doesn't lie in the question "Do diets work or not?" - it goes much deeper than that.
At the risk of alienating one side or the other (and that there are lines drawn between them at all seems silly to me to begin with) I'm going to speak up about this. It seems to me that the root of dieting and the root of giving up on diets altogether is actually the same. There's really no difference between actively dieting or actively "not dieting." Seems strange, but stay with me... it's true. The root of both of these is fear.
Dieting is the fear of being fat, getting fatter, not being accepted - ultimately, it's the fear of dying. Actively NOT dieting on the other hand is simply a denial, and it's the fear of failure and rejection (accept me as I am!) Ultimately it's the fear of the self, of finding who is underneath it all, of discovering what's hidden. (Which is ironic, since the fat acceptance movement is all about loving "what is." Really, it's nothing but loving the denial...)
Okay, I know that sounds harsh. It probably is. But both camps seem to be missing something, don't they? They're at extremes. Which is a famous marker of those who are addicts. Addicts love extremes. Are you a dieter? Then you're going to diet, you may lose weight, but ultimately, you're going to fail. Because diets don't deal with the root cause of your addiction (your fear). It will return once you've stopped "dieting." Are you a non-dieter? Someone who insists diets don't work, I'll never be thin, I'm genetically pre-disposed to be like this, and you should accept me as I am? Then you've simply stuck dug heels in, turned your head, and are denying what's coming. It doesn't make you any less afraid, underneath. It doesn't make death any less imminent.
Nothing does.
And that's the truth that both extremes seem to miss. Neither path leads anywhere different. They're both going to the same place. Different paths, same destination. Which makes them both look sort of silly. Restricting your calories to the point of pain, spending hours on an exercise bike, becoming obsessive about the numbers on the scale... What sense does it make? Or the opposite, living in