Yes, being able to tell apart the feeling, that makes you crave sugar from the felling that tells you that you should eat some flesh to fix your B12 deficieny, isn't easy.
Getting clear about the outcome that you want to achieve with your eating choices is also not straightforward.
Both are skills for which understanding biochemistry is secondary.
As far as I can tell, distinguishing between those sorts of feeling is a matter of accumulated experience. There aren't classes of feelings, some of which are desires for things which are bad for you and others which are desires for what you need.
Another month has passed and here is a new rationality quotes thread. The usual rules are:
And one new rule: