Single doses of zinc sulfate were given to healthy young volunteers, either in the fasting state or with various types of meals. Dairy products (milk and cheese) and brown bread decreased zinc absorption, as indicated by a significant drop in peak serum zinc levels. Zinc absorption was decreased when zinc was given in the fasting state with the same amounts of purified phosphate or phytate as those found in foods above. Experiments in vitro have shown that zinc is precipitated by phosphate and phytate at pH values close to that of the intestinal lumen. Coffee also seems to inhibit zinc absorption.