Here’s one pathway, and I’m sure there are more:
Ultra-processed food are high in carbohydrates, refined sugars, and industrially processed oils. When consumed, they are quickly and easily absorbed by the body causing a rapid increase in blood glucose, easily proven by a CGM. The body responds by producing insulin. High insulin levels contribute to fat cells stocking lipids and also the replication of fat cells.
which are harmless part of human food that has existed for thousands of years
There are almost no whole foods that exist which contain all three major macronutrients, but this is not uncommon in UPFs. Personally, I would just avoid UPFs entirely.



Calories are a unit of heat, and absorbing nutrition is a biological process. Unless you’re a bomb calorimeter, they have very little to do with what goes on inside you after you eat. I urge you to reconsider what food you choose to eat.
You should absolutely desist from saying that other people should not avoid UPFs, because that is a harmful statement in the same vein as “you don’t have to stop smoking.”