Different polyphenols have different binding affinities to iron apparently due to different levels of iron-binding galloyl groups in different polyphenols. The polyphenols in foods with high levels of polyphenols would also bind iron at higher levels than polyphenols of foods with low levels of polyphenols. The point is that different foods with different kinds of polyphenols and different levels of polyphenols can have different affects on iron. However, if all iron is basically complexed with polyphenols due to coffee, tea and/or sodas then foods with different polyphenols and different levels of polyphenols might not make a difference. Fruits and vegetables would seem not to be delivering the real thing as well as Coca-Cola.
A direct connection between the gut and brain and mood is widely accepted now. How signals are sent from the gut to brain and how those signals affect mood has not been clearly established. Levels of aconitase 1 in the gut, activity of the TCA cycle in the gut and regulation of iron regulated proteins in the gut could play a large role in that connection.