Check into what Cancer patients have to do. The doctors want them to eat fatty foods because they lose weight superfast. This means homo milk, etc. So you said your dad likes chocolate syrup with milk. Ok, so go to baskin robbins and buy him a milkshake with 2% or homo milk that uses a nice chocolately icecream (I love chocolate mousse royale from there but it has chocolate chips which might be a pain in a straw so pick a different chocolate). I'm actually experiencing a chocolate craving right now so I might run out and buy a bar of dark chocolate (I don't buy milk chocolate anymore, got used to dark which is mostly cocoa solids anyways). Buy some chocolate milks in a bottle from Hershey etc at the supermarket. Grilled cheese sandwiches on white bread.. a couple months ago I tried making an old 1950s recipe for macaroni and cheese which involved the use of bread and eggs, along with cheese and macaroni. It was rather interesting and very fluffy. I could dig the recipe for that up it was in my better homes and gardens cookbook from the classic recipes section. None of the above is paleo, but your dad is seriously sick and from what I've seen, paleo isn't conductive to weightgain so normal rules don't apply here. He wants high calorie stuff and his personal preferences may be that he's subconsciously aware of it. Oh, and if you buy ground meat for him don't buy lean either, get medium or higher. And of course, have him eat berries and vegs and stuff now and then, might want to steam the spinach or whatever till it's all soft and mushy so it's easy to spoon in. Walnuts are fattening too, so if he still has teeth, a big bag of walnuts will be nice too. I hope noone freaks out about what I just said. Best, P.