How do you reconcile in your own logical mind the 2 following facts?

1Mother's milk is known to have low level of proteins and humans are growing
at the biggest rate of their life while feeding on it.

2humans adults are said to thrive on a hight protein diet.

and thoses 2 other facts

1Humans milk is rich in lactose (sugar)

2Lot of adults don't do well with high carbonhydrates intake

something in me is missing in me to get around that. Help!

Could it mean that we need sugar to grow tissues and proteins for
maitenance?

thanks
Jean-claude