I think orthodox American Christianity lacks a theology of the body or, to put it in a way that does not necessarily separate body from mind/spirit, a theology of the self. Maybe not "lacks" a theology: it does have a theology, but it is not well articulated; it is inconsistent, maybe incoherent; and it may be wrong in large part.
I have thought on and off about this for many years (which, I readily concede, hardly makes me an expert), but what most recently generated some reflection on the issue was seeing so many over-weight people at the Christian Life Conference. (I know. Everyone is groaning. This again.) But I think the over-weight people I saw simply do not connect what they do with their bodies with their calling to be salt and light. I think there is a sort of Gnosticism at work here, a dualism that leads us away from thinking about how we affect our neighbors by how treat our bodies, in this case how we eat.
If every Christian would reduce his calorie intake so that his weight would fall within the mid-range of the charts and if the food that he ate would be nourishing and empty of empty-calories, the demand for medical services would fall, the price of those services would go down, and poor people would be better able to afford those services. Chronic diseases among elderly Christians would fall, reducing the demand on care-givers, nursing homes, and the like, thus reducing the costs of those services, and making them more accessible to the poor. The junk food industry would stop growing and alcohol consumption would go down.
But I hear nothing, nothing about that. I just hear the body mentioned in two contexts: sex and the Lord's Supper (how's that for a combination?).
Sex seems to be the most important thing about the body that Christians talk about. And we talk about it so competently that our divorce rate approaches that of the general population, and we allow the same-sex relationship issue to define whether we are "really" Christians.
As to the Lord's Supper, I come from a tradition where it has been completely and utterly spiritualized. "This is [really not] my body, broken for you."
The Presbyterians, where I presently have a home, are not quite sure about the Lord's Supper. It is a sacrament, not an "ordinance", to be sure. We think something happens. It's not simply a metaphor, as the Baptists seem to believe. But I'm not quite sure that the Reformers completely worked it out. (I could be wrong on this, and I apologize to those in the Reformed Tradition if I am.)
Here is what happens at our church. We "celebrate" the Lord's supper at a worship service once a month. We have little wafers for the bread/body of Christ. We have grape juice for the wine/blood of Christ. (I don't understand the grape juice versus the wine, especially with wine so cheap and plentiful.) Then, after the service, we have a light lunch in the Fellowship Hall. Here's what I think about that: the real Lord's Supper occurs during the light lunch, where our bodies are being nourished along with our spirits through the wonderful fellowship. I would like for the pastor, as the light lunch fellowship begins, instead of saying the blessing, to pick up a sandwich and then a cup of lemonade and go through the litany. (And maybe the deacons would wait on people during the lunch.) Then we would sing a hymn when the lunch is over and go out.
Like a lot of things, the ancient Jews had the body thing right. There is a unity between mind and body. Adultery, being unkind to one's spouse by the use of one's body, is on the same list as having "no other gods before me". Resting on the Sabbath has the same amount of moral weight as does adultery. When the resurrection occurs, the resurrection will be a bodily one. We will have clothes in heaven. We will recognize each other. We will walk on streets. Finally, Christ was not simply God, he was God incarnate.
So eat your vegetables and stay away from the sweets. That would be a righteous thing to do.
UPDATE: American Christians are not entirely bereft of some leadership on this issue, although Mennonites may not qualify as exactly mainstream. And Pam Smith has been featured on Focus on the Family.