The present invention provides methods and compositions for, for example, effecting weight loss and treating excess weight by administering OB protein, or a derivative thereof, in a form for constant supply, for example, continuous administration, at a dosage of less than or equal to about 1 mg protein/kg body weight/day. Compositions and methods used for production of recombinant murine and human OB protein are also provided. Compositions and methods for preparing recombinant murine methionyl OB protein and recombinant human methionyl OB protein, including DNA sequences, vectors, host cells, methods of fermentation, and methods of purification are provided herein.