Doctors I learned Carnivore from, say that there is NO requirement in the human body for carbs at all. That Carbs are addictive and God put them into the environment for a few weeks in late summer every year to fatten up on prior to winter. Carbs were never intended for 365/7 eating. So it is clear that we can function most of the time or exclusively only on animal products for energy and complete nutrition.
We are also designed to be attracted/addicted by Carbs to drive this compulsion to fatten up but nature limited their availability to fruits and veggies for only a short time in the year.