In 1956, I might follow these guidelines to eat like this:
Breakfast:
1 bowl oatmeal, 1 glass milk, 1 serving berries
Lunch:
A sandwich consisting of 2 slices bread, a serving of sliced meat, and a slice of cheese, plus an apple
Dinner:
A serving of meat, a potato, and a green vegetable, plus a dinner roll with a little bit of butter
But you get to the 1980s and we're being told that's not nearly enough food. Eat more and be healthy!