There is no constitutional guarantee for freedom of food, and you are looking at the issue in an incorrect way.

The US Constitution does not grant rights to citizens - it restricts the government from infringing on the rights of the people. Through that document, the federal government has certain powers that were granted to them by the people (Article I, Section 8 - the enumerated powers clause).

Simply put, if the powers are not granted to the federal government by the Constitution or by a constitutional amendment, they don't have the power.

So one argument is that the Constitution does not grant Congress the power to stop people from eating certain foods. If Congress were to pass such a law, it wouldn't be a violation of your rights - it would be an over-extension of Congressional powers which violates the Constitution.

The states can regulate almost anything they want, thanks to the 10th amendment, but the federal government can only do what is listed in the Constitution.

Hope this helps!

EDIT: Some laws are passed by Congress that seem to go beyond their enumerated powers, but the courts have granted them wide berth through the "commerce clause". There are so many arguments for and against Congress using that clause to reach beyond what they are supposed to.