One proposal receiving some attention is to impose a tax on foods that contain high quantities of saturated fat in the hope of cutting down consumption of these foods. The basic law of demand states that a tax on saturated fat would raise the price of fatty foods, and thereby would reduce their consumption. A good analogy is with other "sin"taxes, such as the very heavy tax in most countries on cigarettes, or the large tax in many countries on alcoholic beverages. These taxes have greatly raised the price of these goods and reduced their consumption. For example, it is estimated that every 10% increase in the retail price of cigarettes due to higher taxes cuts smoking by about 4% after the first year, and by a considerable 7% after a few years.
He ends up arguing against the use of a tax on foods with high levels of saturated fat due to the fact that there are other major causes of obesity, the likelihood of future medical advances, and a doubt of whether it would be an effective tax.
(Source: Becker-Posner Blog)