There are some concerns as to how to obtain a wholesome diet if someone is a vegetarian.
I will consider a few points here.
1. Proteins from animal sources (meat, chicken) have a high biological value (B V). The proteins in cereals and legumes have a lower BV. For those vegetarians,who are not averse to eating eggs, this fact is compensated to some extent. Soybeans has the highest percentage of proteins amongst all cereals and legumes, thus more consumption is indicated.
2. Vitamin B12 comes from animal sources (meat). It is not found in vegetable sources. While milk and milk products do provide B12, for vegans (who consider even milk out because it comes from animals) this source is also out. The answer is fortified foods, like cereals which will give you B12.
3. Fish is considered nutritious because it provides rich amounts of proteins and omega-3 fatty acids. For the vegetarians, walnuts (akhrot) and vegetable oils like canola oils will give you omega -3.
4. One aspect about milk is worth mentioning. Although milk is a considered a wholesome item, it is not a good source of iron.