Chris Dillow recently wrote a post— on the subject of Kerry Katona's breasts—discussing self-ownership and utilitarianism.
There's a parallel here with policy towards obesity. Self-ownership says individuals have a right to become lard-buckets. Utilitarianism - the costs to the NHS and the ugliness of our streets - requires that they be constrained from doing so.
But Chris misses a rather crucial point: we do not own our own bodies or our own lives and have not done so since at least 1948. How can I say that? Well, think of it like this.
The state is the provider of a service: the National Health Service in this case. Because the state provides and "pays" (through taxes, of course) for this service, it has the power to dictate to the population.
Obesity costs money over and above a "normal" person's treatment. Even if the obese person has private medical insurance, they cannot opt out of the NHS because they are forced to contribute to the NHS through their NICs. And, in fact, because of various laws—an ambulance can only take you to a state A&E, all GPs are employed by the state—no one can opt out of the state-provided system entirely.
In this way, everyone is in debt to the state. And as long as everyone is in debt to the state, the state, fundamentally, has the right to tell the population how to behave. And this debt can never actually be discharged: you are in debt to—and thus subject to the whim of—the state from the moment that you are born until the moment that you die.
And, remember, there is no actual contract to sign (or not sign) so the government can—and does—keep on shifting the terms of this agreement as and when it likes. It's a little like Lando Calrissian's bargain with Darth Vader in The Empire Strikes Back: "This deal just gets worse..."
As such, no one in this country owns their own body; no one in this country owns their own life. Everyone is effectively in hock to the state because you can never, ever opt out of state provision.