Have a look at this TIME article. The headline is "Americans Are Eating Fewer Calories, So Why Are We Still Obese?".
It goes on to cite two studies.
One study shows that old people eat less fast food then young adults, and that in general food consumption is declining. This comes from the aging population I guess. The other shows a small decline (about 7%) in the calorie consumption of children.
Neither study showed a decrease in calorie consumption by adult Americans, as far as I can tell. The naive assumption would be that consuming fewer calories would result in less obesity, but no data on the topic is presented. The headline is a complete misdirection.
The moral of the story is you should limit your observations to what the data actually says.