It basically is in a fairly straightforward way.

In the Declaration of the Independence it states thusly:

"that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.--That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, --That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness."

Since you cannot have Life without food, it would logically follow that it is the government's job to (secure these rights) food for people. If it does not, then the Declaration of Independence states that we can overthrow the government.