The New York Times has a cool interactive project about what people actually order at Chipotle that, I think, is supposed to shock you with the revelation that the typical order contains 1,000 calories. That's a large meal, no doubt, but it seems to me that a 1,000-calorie meal could easily be one of the three meals consumed in a government-recommended 2,000 calorie day. The problem with this kind of restaurant-shaming (see also this earlier effort from the NYT) is that as best as people can tell eating big meals isn't actually what's driving America's obesity issues.
It's all about the snacks.
The above is a table from David Cutler, Jesse Shapiro, and Ed Glaeser's 2003 study "Why have Americans become more obese" and what it shows is that pretty much all of America's increased calorie consumption between the late-1970s and the mid-1990s came from increased snacking. Women actually started eating smaller meals during this period, they just more than made up for it with snacks.
That data is a little out of date, but according to Professor Richard Mattes the snack explosion only continued. In 1996, the average American ate about 423 calories worth of snacks per day but by 2006 that was up to 580.
The centrality of snacking to obesity is a significant challenge for public policy. There's a lot of focus on chain restaurant portion size, both in the media and in terms of the Obama administration's push for menus to state calorie contents. But the issue really doesn't seem to be that people started ordering gigantic meals. It's more that they started supplementing regular meals with more sweetened beverages and bigger bags of chips. It's noteworthy to me that I see a lot of emphasis lately on fancy places trying to push "healthy" snacks — nuts and dried kale and what not. But it's clear from the data that the actual pattern of the healthier eating habits of yore was simply less snacking rather than a universe of tasty nutritious treats.