Citrulline is one of the several ingredients common at most popular pre-workout supplements. Watermelon is a natural source of it, and other citrulline food sources include peanuts, soybeans, and kidney beans. Citrulline-rich foods also include squash, cucumbers, pumpkins, etc… Its name comes from Citrullus, the Latin word for watermelon, and it is a non-essential amino acid, which means that the …