There are a whole lot of people who have their own interpretations of the commandments, and that coupled with our history of secrecy surrounding the temple could definitely give rise to the idea that it's difficult to know what all the requirements are, but it's all online and available to everyone at this point.
Here's the relevant information about the health code[1]:
> The Lord revealed in the Word of Wisdom that the following substances are harmful:
> Alcoholic drinks (see Doctrine and Covenants 89:5–7).
> Tobacco (see Doctrine and Covenants 89:8).
> Tea and coffee (see Doctrine and Covenants 89:9; latter-day prophets have taught that the term “hot drinks,” as written in this verse, refers to tea and coffee).
[0] https://www.churchofjesuschrist.org/temples/what-is-temple-e...
[1] https://www.churchofjesuschrist.org/study/manual/gospel-topi...