One thing to be aware of for people who choose a vegan/vegetarian diet is that plant foods do not contain Vitamin B12.

Vitamin B12 is an essential nutrient. Vitamin B12 deficiency can have many adverse health outcomes.

There are ways around this - some plant foods have been fortified with it and it can also be taken as a supplement.

This is discussed here How prevalent is vitamin B(12) deficiency among vegetarians? - PubMed - NCBI.