Farnam Street: Sin Tax
Epstein and colleagues simulated a grocery store, "stocked" with images of everything from bananas and whole wheat bread to Dr. Pepper and nachos. A group of volunteers — all mothers — were given laboratory "money" to shop for a week’s groceries for the family. Each food item was priced the same as groceries at a real grocery nearby, and each food came with basic nutritional information.The mother-volunteers went shopping several times in the simulated grocery. First they shopped with the regular prices, but afterward the researchers imposed either taxes or subsidies on the foods. That is, they either raised the prices of unhealthy foods by 12.5%, and then by 25%; or they discounted the price of healthy foods comparably. Then they watched what the mothers purchased.
To define healthy and unhealthy foods, the scientists used a calorie-for-nutrition value, or CFN, which is the number of calories one must eat to get the same nutritional payoff. For example, nonfat cottage cheese has a very low CFN, because it is high on nutrition but not on calories; chocolate chip cookies have a much higher CFN. The researchers also measured the energy density- essentially calories- in every food.The results, just published in Psychological Science, a journal of the Association for Psychological Science, show that taxes were more effective in reducing calories purchased over subsides. Specifically, taxing unhealthy foods reduced overall calories purchased, while cutting the proportion of fat and carbohydrates and upping the proportion of protein in a typical week’s groceries.