The persons can continue a vegetarian diet for different reasons, beliefs, religion, economy, or health, but in any case it must be well informed and knowledge that it offers advantages and disadvantages.
The vegetarian diet must be well raised and to be balanced in components and nutrients. Especially in children and adolescents who are necessary certain essential elements for the growth.
The elements that can be missing in a vegetarian diet are certain proteins, the vitamin B12, the vitamin D, the riboflavin, the calcium, the iron and other minerals.
Between the proteins there is missing usually the called "compline" that are usually in the meats, fish and the eggs and that it has all the necessary amino acids to live.
In the vegetables there are usually "incomplete" proteins, which it has lacking in some amino acids in quantities adapted for the development, for example in the cereals and the vegetables.
It is not also necessary to eat animal products to obtain these "finished" proteins since, on having mixed two vegetable incomplete proteins or it is not possible to obtain the necessary amino acid. For example on having mixed the milk with cereals, lentils with rice, or cereals / pasta with cheese.
That's why a strict vegetarian must do certain authorizations to take a more balanced diet. The vegetarian diets with animal products are more healthy (lactovegetariana and I suckle - ovovegetariana).