Tannins

Tannins are polyphenols responsible for astringency, that dry, rough feeling in the mouth from strong tea, tannic red wine, unripe persimmon and cocoa. They bind to proteins (including those in saliva, hence the astringency).

The two faces of tannins, antioxidant versus anti-nutrient: tannins perfectly illustrate the duality of many plant compounds:

On the beneficial side:

1. Powerful antioxidants
2. Antimicrobial properties (traditionally, tea and wine were « safer » than water)
3. Cardiovascular effects (like other polyphenols)
4. Tea and cocoa owe part of their benefits to their tannins

On the anti-nutrient side:

1. Tannins bind to non-haem iron (from plants) and reduce its absorption. Drinking tea or coffee with an iron-rich meal can significantly lower iron absorption
2. They also reduce (moderately) the absorption of some proteins and other minerals

The timing trick (practical and little known): to get the best of both, simply shift things: drink your tea or coffee between meals rather than with them, especially if you are at risk of iron deficiency (women who menstruate, vegetarians). Conversely, adding a source of vitamin C to the meal offsets the effect of tannins on iron.

A concrete case: someone who drinks tea with every meal and complains of tiredness or low iron would benefit from moving their tea away from mealtimes.

Tannins and wine: the tannins in red wine (from the skin, pips and barrel) give the wine its structure and ageing potential. They contribute to wine’s (hypothetical) benefits, but remember that alcohol cancels out those benefits (see alcohol). Grape juice or grapes provide tannins without the alcohol.

In practice: enjoy tannins (tea, cocoa, fruit) for their antioxidants, while managing their effect on iron through timing (away from meals) if you are at risk of deficiency. A good example of nuance: neither a « superfood » nor a « poison », but a compound to use sensibly depending on your situation.