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.
Tea very significantly decreases iron absorption as tannins in tea form insoluble complexes with iron. Iron in iron/tannin-complexes would also not be bioavailable in the gut. Still individuals who drink tea can have normal iron levels. The question is whether blood measures of iron status are a complete picture of iron status. In the proposed experiment rats would be given tea by gavage. Levels of tea given by gavage would not be levels that would cause anemia. What would be tested is the status of aconitase 1 in the gut and the effect of the tea on the citric acid cycle in the gut. Aconitase 1 is regulated by iron levels where with high levels of iron aconitase 1 acts as an aconitase but with low levels of iron aconitase 1 switches to IRP1 which regulates iron regulated proteins. Levels in the gut of citrate synthase, isocitric dehydrogenase and succinate dehydrogenase would would also be tested as iron positively affects these enzymes also. Blood levels of iron would also be tested. The hypothesis is that the effect of tea on the gut in terms of aconitase 1 and other enzymes in the citric acid cycle will be more pronounced than blood levels of iron would indicate.