On December 7, 2013 I realized I may have been causing myself to have a painful, swollen right knee joint by drinking a daily cup or more of Hippocrates soup. After not drinking it (and not eating anything else made with tomatoes) for just one day my knee felt better and by the end of the week my knee was back to normal.
Tomatoes are in a group of vegetables called night shades. They include tomatoes, potatoes and peppers (but not black pepper). I have experimented by eating potatoes (they are also in Hippocrates soup) and have had no return of the knee pain, however, I ate an enchilada on December 19th and the pain returned immediately. By the next day my knee was feeling better and the next day it felt normal again. Even though I love tomatoes, I will not eat them again.
Here's a good write-up about night shade vegetables: