No food is inherently unhealthy or bad, so I don’t think there’s any issue with him eating McDonalds on a plane. Maybe he was in a hurry, or just wanted to be social and stopped there with someone else who wanted it.
What is unhealthy is when the majority of your food is not nutritious, which is currently the case for most Americans. So why not try to make common American foods more nutritious by default, as they are in most other wealthy countries?
It was awesome living in a European country for a couple of years as an American. You learn that ingredient lists at the grocery store really are shorter in ways you don’t expect. It’s easy to buy a fruit yogurt that is just yogurt and fruit, for example. Not “yogurt, sugar, artificial and natural flavors” as you’ll find in many popular foods in the US. It was noticeable with a lot of different food choices.
Also, whenever we would come back to visit the US, after living there for a year or so, we would always have mild digestion issues and stomach cramps for a week or so. This was common among many expats that we talked to. We visited over a dozen countries while we lived there, and the US was the only one that had that issue.