As Stephen alluded to, the evidence that we do have so far about economic incentives and disincentives suggests that economic incentive is a much better driver for making healthy choices. So lowering the price of healthy food or subsidizing nutritious, healthy food--low energy-dense food--tends to have a greater impact on people's purchases and food-related behaviours.
That may be in part because we haven't made the disincentive great enough to really affect people's behaviour. That's difficult to do, because the more energy-dense foods are much cheaper, so the amount you would have to increase the taxes by, as with gasoline or tobacco, would have to be quite severe.
So yes, economics are clearly an important component of this, and understanding that and collecting the information about how to drive healthy eating and active living is extremely important.