A new paper by Bollinger, Leslie, and Sorenson studies Starbuck’s sales data to assess the effects of New York City’s mandatory calorie posting law.  Here is the abstract:

We study the impact of mandatory calorie posting on consumers’ purchase decisions, using detailed
data from Starbucks. We find that average calories per transaction falls by 6%. The effect is almost
entirely related to changes in consumers’ food choices—there is almost no change in purchases of beverage calories. There is no impact on Starbucks profit on average, and for the subset of stores located close to their competitor Dunkin Donuts, the effect of calorie posting is actually to increase Starbucks revenue. Survey evidence and analysis of commuters suggest the mechanism for the effect is a combination of learning and salience.

And this bit caught my eye:

The competitive effect of calorie posting highlights the distinction between mandatory vs. voluntary posting. It is important to note that our analysis concerns a policy in which all chain restaurants, not just Starbucks, are required to post calorie information on their menus. Voluntary posting by a single chain would result in substantively different outcomes, especially with respect to competitive effects.

A natural response to these laws is that if it were in the interests of consumers, vendors would voluntarily post calorie counts.  But if consumers are truly underestimating calories, then unilateral posting by a single competitor would backfire.  Consumers would be shocked at the high calorie counts at Starbucks and go somewhere else where they assume the counts are lower.