In 1516, the Reinheitsgebot or Law of Purity was decreed in Germany. It is apparently the oldest still-active piece of food health legislation.
"... we wish to emphasize that in future in all cities, markets and in the country, the only ingredients used for the brewing of beer must be Barley, Hops and Water. Whosoever knowingly disregards or transgresses upon this ordinance, shall be punished by the Court authorities' confiscating such barrels of beer, without fail."
However, legal action in Germany with respect to beer dates back to 1165.