Healthy people are good for an economy: they are productive, happy and in particular do not generate (poor) health related costs. As long as all those characteristics are private, there is no need for the government to intervene and promote good health. Everybody is free to choose the lifestyle she prefers, and suffer the consequences.
If there are externalities, it is another story. Second-hand smoke, drunk driving, are all example of lifestyle choices that have a negative impact on others. But health itself also has an impact if health care costs are at least partly carried by the community. This is the case in socialized health care, like in the United Kingdom and Canada, in mandatory group health insurance like in Germany, or in state supported old age health care like in the United States. There are two ways to address this: tax bad behavior, or subsidize good behavior.
Thus the plethora of sin taxes. Among existing ones, let us mention cigarettes and alcohol. But other possibilities could be trans-fat, French fries, corn syrup and sodas. One can also encourage good behavior: some health insurance companies offer lower rates for non-smokers or subsidize various sports activities. Canada introduced last year a tax credit for up to C$500 towards a child's sport activities. There is now a proposal on the table to create a similar tax credit for adults, up to C$1,500.
Telling people to exercise and eat well is only going so far if they are bombarded with temptations. But making them see the consequences in their budget, and early rather than later when they get sick, is bound to have more impact.