The case is New York State Restaurant Association v. New York City Board of Health, decided on February 17. The law "requires roughly ten percent of restaurants in New York City, including chains such as McDonald’s, Burger King and Kentucky Fried Chicken, to post calorie content information on their menus and menu boards." The trade group's First Amendment claim is not necessarily off the wall, but this is a tough argument. Putting aside the settled notion that "the protection afforded commercial speech is somewhat less extensive than that afforded noncommercial speech,” commercial speech enjoys even less protection when the speech is factual in nature, as opposed to a controversial or political statement that the businesses are being forced to repeat. In 2001, the Court of Appeals made this clear:
Commercial disclosure requirements are treated differently from restrictions on commercial speech because mandated disclosure of accurate, factual, commercial information does not offend the core First Amendment values of promoting efficient exchange of information or protecting individual liberty interests. Such disclosure furthers, rather than hinders, the First Amendment goal of the discovery of truth and contributes to the efficiency of the “marketplace of ideas.” Protection of the robust and free flow of accurate information is the principal First Amendment justification for protecting commercial speech, and requiring disclosure of truthful information promotes that goal. In such a case, then, less exacting scrutiny is required than where truthful, nonmisleading commercial speech is restricted.
That block quote is from the Sorrell case. The Restaurant Association argues that Sorrell is not good law because a Supreme Court decision from that same year, United States v. United Foods, 533 U.S. 405 (2001), better governs the analysis. The Second Circuit disagrees, finding that the plaintiff here reads too much into United Foods which simply stands for the proposition that compelling businesses to disclose certain information is legal if it's intended to prevent deceptive advertising.
The City is allowed to compel the restaurants to disclose the caloric content to patrons because the government has an interest in controlling obesity. Under commercial speech doctrine as outlined by the Supreme Court, that qualifies as a "rational basis" for the law which is therefore constitutional and consistent with the First Amendment. In outlining why this law is rational, the Court cites recent obesity statistics and the fact that Americans are eating out more and that fast food restaurants in particular are responsible in part for the obesity epidemic. The City is therefore allowed to require restaurants to help patrons make informed decisions about what they are eating. Indeed, this decision relates quite a bit of statistical information about the negative social consequences resulting from the bad food choices many Americans are making. I would guess these statistics came out of one of the many amicus briefs that were filed in the case. Isn't that what amicus briefs are for?