Sri Chimmoy said that in order to be on the spiritual path it is advisable to be on a vegetarian diet. He explains that when we eat flesh, the qualities (e.g. aggressiveness) of the animals consciousness enters into us. Our vibrations are lowered. That is perhaps why we feel tired after a non-vegetarian meal.
The vegetarian life makes it easier for us to live a life of sweetness, softness, simplicity and purity.
Being vegetarian does not equate to realising God, for that needs aspiration. For an aspirant it is advisable to be vegetarian as s/he is trying to live a life of peace and tranquillity. To eat meat of any kind requires the killing of a being, and act of violence, which is then concealed and presented in nice packaging.
It is not wrong to eat meat. Jesus and Swami Vivekananda ate fish. Some need to eat it and some do not. It is not true that eating only meat will give you strength, power and energy. There are many people who are pure vegetarian or vegan and are strong and healthy. It is peoples own feelings and ideas about food that is giving them the strength. When you aspire properly and meditate you can find out where your strength comes from ... which might take a few years! - excerpts taken from the book “The Wisdom of Sri Chimmoy”.
[A vegan bodybuilding experiment]
Paramanhansa Yoganada recommends that the daily diet should include a percentage of milk and dairy products like cheese and yogurt; raw vegetables, fresh fruits, orange juice with ground nuts mixed in, eat less meat (avoid beef and pork if possible) and fast once a week – from Paramahansa Yoganda's book, “Man's Eternal Quest”
Sathgurunath Yogiraj discusses this topic in a very brilliant, interesting and humorous way in this clip.
Eat what you feel is right for you, however, if you want to be on the spiritual path and be more healthier, it helps to be vegetarian. It is easier to give up meat bit by bit. Start by eating more vegetables and less meat, especially red and processed meat of any kind. Eating oily fish is much healthier. This will be better for your health, the spiritual path and the environment. Watch this Ted Ed clip.