As everything has its own aura. So whatever we eat has definitely some effect on us. If we follow the food chain pyramid, the forms higher up in the pyramid are more and more complex. Therefore consuming higher evolved beings (such as animals) takes up more energy for digestion as compared to lower evolve beings (such as plants). As a result of which the extra energy consumed could have been used by the body in a better way for purification or cleansing purpose or in any other beneficial direction. One might have definitely felt light after having a vegetarian meal in comparison to a non-vegetarian meal.Moreover, the surrounding in which a plant is grown also affects it. When plants are grown in bad vegetation are definitely bad for consumption. Plants grown in a well cared environment yields better, nutritious and healthy produce for consumption.I once used to eat a lot of non-vegetarian food. But one day I lost my appetite for it from within even for eggs. People often ask that how I fulfill my amount of protein requirement and my answer is that there are plenty of alternatives like lentils, tofu, fruits and vegetables. As Shailesh has mentioned that “It is just a part of spirituality. You cannot get spiritually advanced just by eating food.”

Being a vegetarian does help calm the mind. The topic of what to eat and what not to eat is a vast subject hard to explain in a few lines. In addition to what one eats, one's regularity and sincerity in spiritual practice also counts. Now, being a vegetarian helps with the regularity of the spiritual pratice as well, so it is the circle of cause and effect.

I have provided more of my thoughts here.