Carbs are not an essential nutrient. Full stop.

There's a genetic disorder in which the person does not have the enzymes to handle any kind of carb intake, which builds up in their blood and can cause all kinds of mayhem. The treatment is to not feed the child anything with carbs, a very ketogenic diet. Provided this is started early enough, the child grows up fine.

Because they don't NEED the carbs. No one does.