Weird choice of the image by TheGuardian: there's some obviously highly processed foods such as doughnuts and candy, but you also have french fries, popcorn and even some nuts there. The text itself doesn't elaborate on this much either.
What is it exactly that I am supposed to avoid?
The easy answer that encompasses 99% of the target foods is:
Avoid any foods that involve multiple rounds of processing, a term that includes baking, frying, adding preservatives,sugars or oils. Generally, if it has a lot of sugar or oil and has a weirdly long shelf life, be suspicious.
Drift towards: easily washable (smooth/peelable) fruits and vegetables, 100% whole wheat bread products, simple meat products like whole animal parts or deboned animal parts.
Dairy lives in the middle ground. If you have zero lactose problem, most dairy is mostly okay, just watch for sugar levels and recognize that most dairy products are calorie dense. Nuts are in this group too for the same reason but oil instead of sugar.
Bonus points for consuming real pro and pre biotics when you can. In the United States this is pretty limited to live culture yogurts, refrigerated kimchi, and refrigerated sourkraut.
Hang on. Pickling and fermentation are multi-step processes to transform food into their final state. Moreover, pickling is expressly used for preservation and long shelf life. Why are they not considered "ultra-processed" according to this definition? As you point out, they are an integral part of a healthy diet in multiple cultures.
Because the "Ultra-processed" definition is backwards. It's really more "foods that have statistically significant negative effects on health" than a description of why they do so. Because we don't yet know why they do so, and there are probably multiple causes. It seems like modern processing methods create this property, likely in part because the results are hyperpalatable. "Foods that are bad for you are bad for you" is tautological, so the ultra-processed naming is used for the hypothesis that it's something about the processing that makes them bad for you. This hypothesis seems highly likely, but we don't know what propert(y|ies) of the processing cause the harm, so it's a bad name but useful for discussing the hypothesis.
But this definition isn't right. UPFs do have a pretty widely recognized definition (the nova classification) and one of its major criticisms as a useful categorization is that there are plenty of junk foods that aren't UPFs.
> but you also have french fries, popcorn and even some nuts there
For popcorn at least, I'd assume it's the prepackaged microwavable popcorn that gets flagged as UPF, where it's encased in hydrogenated oils, salt, and preservatives. It's hard to think that popcorn you make at home could be considered UPF, considering that it's literally one ingredient with heat applied to it (and oil I guess if you're popping it on the stovetop rather than an air fryer).
