I think a lot of it depends on the person and what they LIKE to eat. I found that "comfort" foods were something I really wanted like my grandma's meatloaf or my dad's tomato soup, lol. I had a had time eating because of the radiation, not the chemo. Now I have had a hard time starting to eat again as I got so used to NOT eating, lol. Last Dr.s visit his nurse took one look at me and said "Get your a** up on that scale!!" She and I have always had a good rapport, lol and she knew I had not been eating like I should. Made it easier to order the brownie delight for dinner the other night though, lol.
Your Dad will let you know what he wants to eat but have a wide, easily prepared, variety of foods available for him.
God Bless,
MO