Try to imagine what it was like in the earliest days: everyone knew you had to eat to live, but what happened to the food? And what KINDS of food were necessary? Why? No one had any idea. For example, in the 18th century orphanages would feed pap, a mixture of cooked cereal and water, to infants. They expected it to be suitable because it was white and fluid, like milk. Why the babies invariably died was not understood, but inadequate nutrition was not suspected.