A common idea in the vegan community is that breast milk contains only 5% protein and babies double in size rather rapidly on this small amount of protein. So we only need 5% protein max right?
Indeed breast milk contains only 5% protein roughly, but 5% of what? The problem with this is people assume babies consume the same amount of calories per kilogram of body weight as fully grown adults. They do not. A well fed baby consumes on average 120 calories per kilogram of body weight per day. An adult consumes roughly 35 calories per kilogram. If a grown adult was consuming as much per kg as a baby they'd be consuming somewhere between 8000 and 9000 calories a day. If 5% of those calories were from protein you'd be getting over 100g of protein. The RDA is only 56g for the average male or 44g for a female. Put another way babies get more protein per kilogram of body weight a day. Roughly 3 times more. So this idea doesn't really help anyone figure out adult protein requirements.