[Disclaimer: yes, dieting serves many legitimate health-related functions.]
For many of us trying to lose weight, health is not the problem. My health is just fine. But college leads to late night studying which leads to stress which leads to junk food, which leaves me making good resolutions and more or less carrying them out.
Then my read-the-Bible-in-13-weeks plan got me into Matthew, and something in the Sermon on the Mount lit up in a new, possibly weird, but very humbling way.
"Therefore I say to you, do not worry about your life, what you will eat or what you will drink; nor about your body, what you will put on. Is not life more than food and the body more than clothing?" (Matt. 6:25)
Food shouldn't be the point, whether the problem is undereating as a way to fit into a smaller pair of pants or overeating as a substitute for true community. Stop worrying about how many calories in your lunch are from fat, stop making chocolate the answer for a long day at work, and seek the kingdom of God and His righteousness.