A diet rich in anti-oxidants, which, a number of nutritionists claim, may help to strengthen the immune system.
Is "which" necessary or why not?
closed as off-topic by starsplusplus, jimsug, Em1, Chenmunka, FumbleFingers Jul 21 '14 at 13:21
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If you leave out "which", the sentence makes sense.
With "which" present, it is grammatically incorrect. It needs a further phrase after "the immune system".
e.g. A diet rich in anti-oxidants, which a number of nutritionists claim may help to strengthen the immune system, can be easily achieved by drinking copious amounts of red wine.