The New York Times reports that, based on several indicators, the average number of calories that Americans consume each day has fallen significantly since 2003 after rising during the prior two decades. "As calorie consumption has declined," the Times notes, "obesity rates appear to have stopped rising for adults and school-aged children and have come down for the youngest children, suggesting the calorie reductions are making a difference." As for what caused the drop in calorie consumption, the Times credits "public health campaigns in recent years" before conceding that such an explanation is temporally improbable, since "the timeline of the calorie declines suggests that people started eating a little less before policy makers got involved."
The Times notes that "the Affordable Care Act, passed in 2010, required chain restaurants to publish the calorie content of their meals." But that mandate has not taken effect yet, so it seems unlikely that it contributed to the decline in overeating. Likewise Philadelphia's produce subsidies, New York City's restrictions on food served at day care centers, and Berkeley's tax on sugar-sweetened beverages, which the Times also mentions but which are too recent and too local to account for a nationwide trend that began in 2003.
Two events that the Times mentions did occur before the decline in calorie consumption began: the 1999 publication of a CDC study featuring "bright blue maps illustrating worsening obesity rates in the 1980s and 1990s in all 50 states" and Surgeon General David Satcher's 2001 "Call To Action To Prevent and Decrease Overweight and Obesity." While the timing is more plausible, I doubt that the general public paid much attention to either of these purported milestones. Possibly Americans figured out that they and their children were getting too fat without the help of public health bureaucrats.