Cup of tea inhibits uptake of mercury from fish
Fish is healthy, but then again it's not. Fish is a source of omega-3 fatty acids, selenium and taurine. All healthy. But because of the cavalier way we treat the planet, fish is also source of mercury and other heavy metals. Not so healthy. So should you eat fish or not? Researchers at Purdue University have come up with a good solution: eat fish and drink a cup of tea with it. This way your body won't absorb the mercury from the fish.Mercury
Even small quantities of mercury are bad for the heart and blood vessels. Fish itself is good for the heart because it contains taurine-rich protein and omega-3 fatty acids. But some studies have shown that because of mercury contamination fish does not always have positive effects on the cardiovascular system. [N Engl J Med. 2002 Nov 28;347(22):1747-54.]

The researchers wanted to know if this situation could be remedied by eating fish in combination with plant fibres or polyphenols. It is known that these inhibit the body's absorption of heavy metals such as cadmium. In Food Chemistry the researchers describe experiments they did in which they digested polluted mackerel 1ppm mercury in an artificial digestive system, complete with all the enzymes and juices that are found in the human digestive system. Then they measured how much of the mercury was converted into a form that the gut cells could absorb.

The results produced the figure below, which tells us that soya protein inhibits the conversion of mercury into an absorbable form. The line shows the amount of mercury, the bars show the amount of absorbable mercury.

Of course a system like this is only an approximation of reality. And the researchers are aware of this. "Further studies, combining a human intestinal cell model with testing in an in vivo system, are required", they write.
When researchers write something like this, it usually means they've already done the research. Often they've already even submitted it to a journal. And that's the case here. The results of the research have already been published in the form of a poster on the Fish4Health website. [Offline] The researchers added human gut cells to their system and then looked at how much mercury they absorbed.
Black tea is the best inhibitor of mercury, the results show. Green tea comes second.

Wheat bran does a reasonable job, oat bran works a bit and psyllium fibre supplement doesn't work at all.

So if you want to be absolutely sure that your fish is mercury-proof, make sure you eat a slice of wholemeal bread along with that cup of tea.
Food Chemistry 112 (2009) 4650.