I know that this may sound "earthly," but I also think that it is good for the children of God to be good stewards of the bodies that belong to the Lord. After all, our bodies are the Temple of the Holy Spirit.
There were very careful parameters to be followed in regard to the original Temple (and Tabernacle). God's Temple was not supposed to be abused, neglected or even garnished with graffiti (tattoos?).
Not only should we avoid gluttony, but, as Greg pointed out, we should avoid any desires that stray from contentment. This is the great flaw in the "prosperity" movement. It is teaching the people of God to long for and greatly desire the excessive things of this life.
Regarding the neglect of the body...
I suggest that believers do what they can to remain healthy. Yes, there are legitimate and varying reasons why some people can be overweight. It is a product of age (which is typically a result of less physical activity). Our modern society provides jobs that can make some people gain weight simply by working behind a desk...using elevators/escalators...or getting around by automobiles.
To counter such things, it is a good idea to maintain healthy physical activity.
Believers can walk, jog, run, and even ride bicycles. If you can't get out and about, I suggest engaging in physical activities indoors. I suggest an elliptical machine. An elliptical machine can be better than a treadmill (or even regular outdoor walking or running). An elliptical is easier on the joints (knees, feet and hips) and is self-propelled (it doesn't run on automatic like a treadmill). As such, an elliptical machine is very quiet.
My wife and I have an elliptical machine, and we listen to SermonIndex messages as we use it. Both of us have always been thin, but we quickly noticed a tremendous difference in our bodies. Not only did we trim excess "newlywed weight" -- but we also noticed that we had more energy, stamina and even our thoughts seemed clearer. Listening to various messages or praise/worship music makes the time seem to fly by! I know this sounds funny -- but I have been touched by God while on the machine. I can't count the times where I was moved to tears while I was jogging on the elliptical -- either by a revelation from one of the messages I was listening to, worship or just praying as I ran/jogged/walked.
Of course, it isn't a sin to be overweight. There are legitimate reasons that are beyond our control. However, laziness and gluttony are sins. By working (or working out) by the sweat of our brow, we can buffet our bodies into physical subjection as we also do this spiritually.
May the Lord bless each of us as we maintain the Temple of the Holy Spirit in the wilderness of this world.