Cranky Flier offers a really interesting chart on airline per-passenger food spending over the past 20 years.
The drop in food spend during the current decade is even bigger than the chart makes it appear, because the figures aren’t adjusted for inflation.
United spends the most on food, with their large international premium cabins and large domestic aircraft flying cross country routes. And that’s before the recent improvement in onboard offerings.
And as Cranky observes, and as in everything else, United does what American does and vice versa.