Kind of a catch-22. Accommodating to altitude is much easier with good nutrition and hydration. But at altitude, food and water (especially that iodine-tinted filter water) are so unpalatable. When your mouth and stomach are uninterested in food, getting adequate calories is a chore.
My last big trip I found that nabisco ginger snaps work pretty well (and they are indestructible in your pack). In fact, I survived 3 days on little more than ginger snaps and hot tea.
So what have people found goes down easy at altitude? What tastes good when you are nauseous?