There are a lot of articles/books along these lines: do some weird thing for a week or a year, log everything, describe what you learned. I tend to prefer the one or two week experiments over the month or year long experiments. Probably because there isn't THAT much to learn over the longer length of time and yet the word count goes up so much.
Predictably, the woman who undertook this experiment discovered that keeping sodium to a reasonable level was basically impossible with this plan. She _did_ discover some other things as well.
(1) Customizing helps. I'm not sure I've ever been to a Taco Bell, so I didn't know about the Fresco option (swap the cheese, sour cream and rice for pico de gallo, is how she describes it -- it may be more complicated than that).
(2) Choosing healthy options such as salads, kale style, etc. results in undershooting on calories. I have a theory about this: the only people who historically have been eating this kind of fast food were mothers of children who wanted fast food, and the mother had given in and eaten there also. And she was perpetually dieting. The 1200 calories plus or minus that the author keeps winding up at (she wasn't aiming that low) is roughly in line with what a dieting boomer woman would have been shooting for over the course of a day in the past.
(3) KFC's problems are worse than KFC realizes. In her case, she discovered she couldn't swap the sides for healthier choices, which imo would explain right there why KFC has been having so much trouble with younger customers. No customization, no healthier choices is lethal. But then on top of it, she ordered grilled and was served fried. W.T.F., KFC? I don't think I've ever eaten at a KFC, either.
And yes, fast food IS cheap and convenient.
I'm super happy that Kate Taylor did this and wrote it up in an engaging and thoughtful way. Fast food should be able to produce real options (enough calories, not such insane amounts of sodium, some degree of customization to cope with dietary constraints whether religious, allergy, lifestyle, etc. in motivation). And several chains are really working hard to accomplish this. If we as a society are going to be eating out with $.50 out of every food dollar spent, then fast food needs to meet some kind of minimum health bar. But as long as we keep pretending that fast food is some kind of guilty side thing that isn't part of our Real Food Supply, the pressure to make this happen is going to be erratic and ineffective.