Tannin

An article, in New Scientist, attempts to discuss why (usually this would only be “how”) the Mediterranean Diet may, or may not, be beneficial.
The mention of nuts in the diet was glossed over, as an assumption, I reckon, that it was probably the oils in nuts, which were beneficial. Having just tried to take the bitter skin of a load of hazelnuts, I think they’ve must a trick. The bitterness is I assume down to the tannin, which many plants exploit as a fungicide. We enjoy our Indian tea, because of that bitterness, although it may be diluted by milk, or masked by lemon, bergamot, or sugar.
We are told that the tea is also good for us.
Maybe, again, it’s the tannin.