marathon running and a vegetarian diet.

That "not consuming enough protein" thing is a myth. Most people get too much protein from the standard american diet (SAD) and that leaches calcium from their bones. (dairy protein)I know a body builder that only eats fruit. He's a fruitarian.
If you eat fish, you can get extra protein from that, like salmon, tuna, etc. Most greens supply adequate protein and calcium. Potatos are high in protein. Nuts are high in protein.

to eat fish would not be a vegetarian. there is a plethora of meat substitute products available from most grocery stores. Morning star farms makes some great tasting products. I'm truly hooked on them and they have as much, (if not more) protein than a lot of their meaty counterparts