Welcome to Gaia! ::

well youve come to the right place =P
I myself have taken a couple of nutrition classes in college. So luckily for you there were some women runners that were on my team in that class! So my professor was also a runner so she liked to pick on us two and use us as examples for things such as what you are talking about.
Well the main thing that you should be worried about is the the nutrients and vitamins that you are not getting from meat products. There are ways to supplement some of them but ill tell you this with a stern warning, supplementing is not ment to be a back door for your diet. They really can harm you badly if you misuse them incorrectly. I would talk to your doctor about your perdiciment before you start supplementing some Vits/Mins. But my real other concern is your auctual protein intake and what exactly you are eating to get those proteins. You being a vegetarian you should know about the 20 proteins you need 11 being made in your body already, 9 being needed from your diet (diet as in what you eat). If you are a runner and you dont get all the proteins needed from your diet and you go on some major race, your body will look for other means of energy to use to keep you going. And when it cant find where it might be normally, what your body does is it converts your proteins being made from your body into energy. What those proteins are usually being used for is building muscle, making blood cells, builds immune, KEEPS YOU ALIVE pretty much.

I'm not an expert but I think it is possible. I'm one of those people that eat, and eat, and eat, and dont gain a single pound and the only reason im having problems is because im having some knee problems.