Cheap (and even not so cheap) "Mexican" food in particular is a great opportunity for the restaurant to bulk up a little protein with lots of cheap filler like rice and beans. With a burger, you have a floor set by a certain weight of ground beef. And, yes, while I very rarely go into a McDonald's or Burger King, my sense is that they're not a particularly cheap meal. And the better "fast casual" burger chains certainly are not.
> bulk up a little protein with lots of cheap filler like rice and beans
Rice and beans make a complete protein. You're writing as if people are getting less protein than they expected, but the inclusion of beans means they're probably not.
You're right of course. I'm just using protein in the sense that restaurants often do to mean x grams/ounces of meat, chicken, pork, or fish. But there are obviously other sources of protein.
