Beware of Milk

I don't have lactose intolerance, my Irish descent protects me from the damn thing. In fact, I've always been able to drink whole milk even in my adult life.

I've been sick for two days, and couldn't figure out why. I went through my food journal and I couldn't understand the reason, yet. Then, I had the light went on when I was in the bathroom.

I thought skim (fat free) and partially skim (low fat) milk were ok, while whole milk had to undergo to a dilution. I had not considered the cooking method!
I've been sick because I've eaten cappuccino (that is, coffee and heated milk). I couldn't make sense of it because the milk was either low fat or whole but diluted with coffee.

I think the mechanism is that the heat changes the fat structure. I still don't know how, but having a milk and coffee with whole milk gives me zero problems.