Menu Mandate's Missing Math

"We were not expecting to see miracles," a health department official told The New York Times. But it's hard to see how such weak results -- which may not even represent net reductions, since people could easily make up for fewer calories at Starbucks by eating more elsewhere -- can possibly stop 150,000 people from becoming obese and prevent 30,000 cases of diabetes over five years, as the health department predicted last year. Nor are they likely to translate into an average weight loss of 3 pounds a year, as the California Center for Public Health Advocacy claimed in pushing that state's menu mandate.

Press coverage of the health department's study emphasized a seemingly more impressive finding: Diners who said they saw calorie information and used it in deciding what to eat -- 15 percent of all customers -- consumed 106 fewer calories than the other diners. But that difference cannot be attributed to the menu mandate, since diners who use nutritional information are apt to be the ones who were most calorie-conscious to begin with.

Such customers had this information even before New York decreed that it appear on menu boards, since fast food chains were already providing calorie counts on their Websites and on posters, tray mats and flyers in their restaurants. The impact of making the numbers more conspicuous was therefore limited to the customers who were least inclined to use them, and the same will be true if a similar menu mandate is imposed nationwide.