"The most concerning problem with 'fat taxes' and 'thin subsidies' are the regressive effects that arise because of dietary patterns that exist before the regulation is enacted."

Can We Nudge, Instead Of Regulate, Our Way Out Of Obesity?

"In the case of obesity, the costs are not completely internalized by an individual because taxpayers fund almost two-thirds of medical costs. The spillover effect associated with obesity increases with government spending on healthcare, and outlays for health programs as a percentage of GDP is at an all-time high of 6.6%.

The economist’s classic response to these concerning numbers are taxes and subsidies. Unfortunately, the traditional approaches appear to fall short in successfully addressing obesity. The most concerning problem with “fat taxes” and “thin subsidies” are the regressive effects that arise because of dietary patterns that exist before the regulation is enacted. People with lower income tend to eat a less healthy diet, and therefore fat taxes increase the prices paid by low income households and decrease the prices paid by high income households. Thus, the subset of the population who can least afford to bear the burden of regulation from fat taxes are forced to unduly absorb more of the cost while collecting less of the benefit."