Which part of the US constitution delegates the US federal government the power to establish the agency "Food and Drug Administration"?
The long title of the 1906 act that established the FDA is "To prohibit the movement in interstate commerce of adulterated and misbranded food, drugs, devices, and cosmetics, and for other purposes."
The reader may note the phrase "interstate commerce", which is a power granted Congress to regulate in Article 1, Section 8, Clause 3.
On a related note since the FDA get its authority from the commerce clause they do not have any authority in non-interstate food issues. Specifically since I was researching sausage, meat products must meet all FDA rules to be transported across state lines for sale, and all facilities involved in the handling of such meat must be inspected by the FDA. On the other hand custom processors (those who butcher meat from hunting) and farmer's market butchers may refuse inspection and have the FDA inspectors arrested for trespassing if they try to inspect anyway. In the case of the custom processor this is because although the meat may have crossed state lines and may again, it never is sold and in the case of farmer's markets although the meat is sold it never crosses state lines.