> avoiding UPFs would likely make the average person healthier

UPFs are defined in a way where you could replace them with essentially identical foods that only count as "processed" by swapping out a couple ingredients with nutritionally identical ingredients (e.g. replace HFCS with sucrose).

The research on UPFs doesn't actually compare ultra-processed food with similar "processed" foods.

So if you replace a pie containing HFCS with a kale salad, yeah it's probably healthier, but there isn't really evidence that replacing an "ultra-processed" pie containing HFCS with a home-made "processed" pie containing sucrose that otherwise has the same nutritional content is healthier (there is some researching showing that fructose can be harmful but the glucose/fructose content of HFCS isn't significantly different from sucrose).

If there is no direct comparison between similar ultraprocessed foods and processed foods, the research doesn't actually show that ultraprocessed foods are bad in a way that homemade processed foods aren't, in which case I'm not sure what the point of defining ultraprocessed foods as a separate category is.

> there is some researching showing that fructose can be harmful but the glucose/fructose content of HFCS isn't significantly different from sucrose

Indeed a lot of people ignore this. Still it is worth pointing out that

a) a higher glucose content due to sucrose based sweetness helps absorbing fructose in a home-made cake.

b) the ultra-processed cake likely got added a fair share of sugar alcohols (keeping it moist) which for a single digit percentage but still significant portion of the population interferes with fructose absorption leading to fermentation in the gut.

c) the longer and cold storage of the industrial cake will lead to an increase of recombined starch which is harder to digest.

(a, b due to fructose transport from gut less efficient than for glucose and the transport part relying on presence of glucose. Some people suffer from fructose mal-absorption where the main transport mechanism is not working and the backup mechanism can be blocked by sugar alcohols)