I love a nice big glass of ice cold milk. Crack an egg in it, add a couple of handfuls of fresh spinach, blend and you'll be good to go on fiber and iron.I've never tried protein shakes, but I use a glass of milk for the same purpose.
Cow's milk is not a perfect food for humans, but last time I checked it could give all my protein with about half my calories and a reasonable selection of other necessary things. (The protein/calorie ratio obviously changes depending on the fat content of the milk, and the activity level of the person.)
The most obvious problem with cow's milk for human food is that it's low in iron, and has no fiber at all. So if I'm going through a stretch where I drink a lot of milk, I make an extra effort to have iron-rich and fiber-rich foods at reasonable intervals.
