Or tax junk food companies.
That won't work, they'll just pass the charge onto the buyers.
That's the point...
Edit:
Longer explanation: As a general principle of economics there is a certain price where every buyer will eventually stop buying, so as price rices overall quantity demanded always decreases. The government can't tax fat people, that is discriminatory and would be terrible PR for the elected officials involved. By taxing companies that produce unhealthy food, the government can kill two birds with one stone. On the one hand, it looks good because it's punishing companies that do not consider health a top priority (i.e. tax for using grease instead of vegetable oil) so it's a win for the FDA, HHS, or whoever else gets involved, in that regard. The real benefit of this is that it will cut out some buyers at varying price points, especially if a healthier option is available cheaper. For example, if baked chips are cheaper than fried chips. Eventually companies will be forced to produce healthier goods. Even if they don't, some percentage of consumers will stop or reduce their purchasing of junk food items. The government can also use the money from the tax to fund a government subsidy of fresh, healthy foods. The idea is to reduce the price of healthy foods and increase the price of junk foods.
Of course there will always be people who want junk food, but they are most likely a lost cause in the end. The key is really to reduce the consumption not eliminate it. Everything is fine in moderation.
