Actually, according to the Nova Wikipedia page, the packaging of potato chips would push them into UPF. The actual, non-edible bag with the slogans and other soothsayings.

Where do you see that? My understanding is that packaging has to actually be implied by the food. It would be psychotic for potato chips served in a paper bag to be okay and potato chips served in a branded bag to be bad but I've been surprised before.

It is the case that several of the prominent voices against UPFs have said some ridiculous things in this direction. Like that a packaged lasagna that is made entirely from ingredients and processes that a home cook would use to make lasagna is bad because it comes from the same corporations and market forces that also produce the frozen lasagnas that are loaded with stabilizers and added sugar.

There have been several cases of possible or confirmed endocrine disruptors in food packaging, such as phthalates and bisphenol-A. My personal opinion is that those probably will turn out to have been harmless, but concerns over them aren't psychotic.

Reference [10], “sophisticated packaging, usually with synthetic materials“

Hold on, is the argument here that a bag is "sophisticated packaging"?

The bags normally used for potato chips are laminated from typically about four layers, one of which is a vacuum coating of aluminum and another of which is polyethylene terephthalate which has been strained to work-harden it, and hermetically sealed with industrial machinery that heats the bag to the melting point of its innnermost layer, typically with an inert atmosphere inside. Potato-chip bags are probably the most sophisticated packaging used for any food you see routinely.

> We have this (reasonably) rigid definition that grants the appearance of specificity. But there are almost surely UPFs that are fine and there are probably non-UPFs that cause the same problems as UPFs.

Not "almost" or "probably"; both are certain: Any description of reality fails on those standards. Always, there are exceptions and edge cases: 'We have this (reasonably) rigid definition that grants the appearance of specificity. But there are almost surely X that are fine and there are probably non-X that cause the same problems as X.'

To meet your standards, we would need a list of every food and its status - and that couldn't be created without impossibly extensive research.

That's why humans use imperfect models and categories - reality is too complex. The most specific, usable category seems to be 'ultra-processed foods'.

> So what is the benefit of saying "avoid UPFs" over "avoid junk food?"

Good question. Both categorizations will be flawed, but maybe UPF is a better fit or easier for people to understand.