The present invention provides methods for using human placental alkaline phosphatase or an active derivative to reduce blood glucose level in a mammal. Treatment regimens provided by the invention may be used to control Type 1 and Type 2 forms of diabetes in humans. The methods and treatment regimens may be effective to maintain the human's blood glucose level below about 10 mM, and preferably within the normal range of 4 mM to 7 mM. The methods and treatment regimens may be used in combination with administration of known anti-diabetic medicaments. Also provided by the invention is a method for inducing weight loss or reducing an expected weight gain caused by or associated with obesity or Type 2 diabetes. The invention further provides a preparation for administration to a human, the preparation comprising homogeneous purified human placental alkaline phosphatase in a physiologically acceptable carrier.