The Mediterranean diet was made up of whole cloth by Ancel Keys, who enjoyed holding nutritional conferences on the European coast (
Big Fat Surprise, N.Teicholz). I guess you could cobble one together with fish, lamb, pasta, fruits and vegetables, and goat- and sheep's-milk dairy.
I found a vegan diet disastrous, personally, with its glaring nutritional deficiencies. Luckily, I felt ill effects after only a couple of months, so didn't do much damage. I enjoyed my vegetarian fare, and ate lots of eggs and cheese throughout.
Recent research in the field shows that individual gut biomes are key to each person's optimal nutritional profile. From what I can tell, omnivory suits me best--no one kind of food is problematic, with the possible exception of bread in large quantities. I plan to give carnivory a run, but I expect it to be rather boring for the long haul. Eventually, we'll have a "gut-check,"
and receive a personally-tailored eating plan, I predict.