The federal requirement that chain restaurants include calorie counts on their menus took effect yesterday, and FDA Commissioner Scott Gottlieb was so excited that he got a bit carried away in describing the evidence that such mandates make people thinner. "We know that providing calorie information on menu labels actually inspires consumers to make smarter choices about overall consumption, when they want to," Gottlieb told The Washington Post. "It does reduce overall caloric intake. Studies show a reduction of anywhere from 30 to 50 calories a day, on average, for consumers who are eating out."
That article links to a February 2018 analysis in the Cochrane Database of Systematic Reviews, the conclusion of which is not nearly as confident. "Findings from a small body of low-quality evidence suggest that nutritional labelling comprising energy information on menus may reduce energy purchased in restaurants," the authors say. "Additional high-quality research in real-world settings is needed to enable more certain conclusions."
A December 2017 review in the journal Obesity was similarly tentative. "Because of a lack of well-powered studies with strong designs, the jury is still out on the degree to which menu labeling encourages lower-calorie purchases and whether that translates to a healthier population," the authors say. "Although the limited existing research finds little evidence of menu labeling shifting fast-food purchases, there are more promising findings that it may influence consumers at certain types of restaurants and in other types of establishments such as cafeterias. It is difficult to know what a meaningful reduction in calorie intake amounts to, particularly when it is hard to measure how people compensate over the course of a week."
Gottlieb, by contrast, asserts that requiring calories counts "does reduce overall caloric intake," which none of these studies shows. Even the studies that report a small decrease in calories purchased cannot tell us the net effect, if any, on total consumption in any given week or month. Yet Gottlieb goes on to calculate that "over the course of a year," 30 to 50 fewer calories a day "could translate into three to five less pounds gained," which "could go a long way toward reducing childhood obesity."
Or not. Gottlieb can be a cheerleader for paternalistic schemes or a scientist offering an honest assessment of the evidence. He cannot be both.