Right I've heard of those examples, but they have nothing to do with diet.

So when people say 'eating sugar causes inflammation' what do they mean? How is THAT inflammation felt?

Bad diet causes brain inflammation. You don't feel pain in this case, but you feel tired and hungry, because the part of the brain getting inflamed specifically regulates metabolism and appetite.

We know there is inflammation there because the brains immune system goes apeshit, and we can see this under the microscope. Gliosis is the technical name.

From my own experience, when I eat too much food that contains high amounts of sugar, I start feeling like I’m getting a cold. I get a sore throat, feel much less energetic, like my body is fighting a disease, skin on my head starts itching and turns red, my nose starts shedding. The symptoms get worse when I keep eating high amounts of sugar. When I feel an onset, I avoid sugar to starve the inflammation.

High amounts of sugar that trigger the symptoms means >100g in 24 h or >60g per day over several days. The effect also depends on the food, probably because of how it is digested. Sugary water (fruit juice, soda) is worse than solid meals. Some forms of sugar are worse than others, e.g. I can eat some chocolate in moderation but others (e.g. Milka) I get a soar throat within minutes of eating a single piece (<10g).

> Right I've heard of those examples, but they have nothing to do with diet.

They do, in fact; a pro-inflammatory diet makes the threshold at which symptoms are felt from any of those other source lower, because inflammation has a substantial systemic component.

(It may produce unique symptoms of its own, too, but I think the main dietary concern with inflammation is systemic contribution to lowering thresholds to inflammatory symptoms when other triggers are present.)