I've never heard that doing any cardio exercise "eats" arm muscles ... a lot has to happen for a muscle to begin degenerating or for your body to start using it as enery ... and I doubt very many people push themselves to that limit. In any event ... when I was focusing on muscle building I ate a lot of tuna fish, cottage cheese and eggs (about 10 a day, half just whites, half with the yolks) ... A lot of people also think a spoonfull of peanut butter a day is a good idea ... But cottage cheese before bed is really a good idea because the protein in it is "burned" slower by your body so you're less likely to produce a defecit during the 8 hours you're sleeping.