I was vegetarian for 20 years (no dairy, no red or white meat) and recently gave it up when I discovered I had hypothyroidism and infertility issues.
In traditional societies, fasting from meat (vegetarism) was meant to be a short term cleansing ritual that could provide health benefits to those suffering from cancer, kidney problems, gout, etc. Long term abstinence from meat has been linked to nutritional deficiences in essential fatty acids, protein, betacarotene, minerals, and vitamins (esp B's).
I suggest that you have a look at "Nourishing Traditions" cookbook by Sally Fallon before subscribing to a particular diet.