Can't help with the US/FDA one (at least not without more digging than I have time for right now), but for the EU the definition is effectively in Article 2 of Regulation (EC) 178/2002:
Definition of ‘food’
For the purposes of this Regulation, ‘food’ (or ‘foodstuff’) means any substance or product, whether processed, partially processed or unprocessed, intended to be, or reasonably expected to be ingested by humans. ‘Food’ includes drink, chewing gum and any substance, including water, intentionally incorporated into the food during its manufacture, reparation or treatment. It includes water after the point of compliance as defined in Article 6 of Directive 98/83/EC and without prejudice to the requirements of Directives 80/778/EEC and 98/83/EC.
‘Food’ shall not include:
(b) live animals unless they are prepared for placing on the market for human consumption;
© plants prior to harvesting;
(d) medicinal products within the meaning of Council Directives 65/65/EEC (1) and 92/73/EEC (2);
(e) cosmetics within the meaning of Council Directive 76/768/EEC (3);
(f) tobacco and tobacco products within the meaning of Council Directive 89/622/EEC (4);
(g) narcotic or psychotropic substances within the meaning of the United Nations Single Convention on Narcotic Drugs, 1961, and the United Nations Convention on Psychotropic Substances, 1971;
(h) residues and contaminants.