Is There a Risk of Deficiency in Carnivore Diets?

i see more and more of people turning to things like, whether it be vegetarian or vegan diets. Are there an increased risk for deficiencies in either of those two cases? And maybe also let's touch on things like polypenals and pito nutrients and am the role that they play in health. i want to be really clear here, because i don't think most people do significantly restricted diets for fun.