6 down
Fig,
pear
almost
turn
out
to
be
the
possible
basis
of
fad
diet
(10)
Fig, pear almost turn out to be the possible basis of fad diet (10)
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hints
The definition is at the end of the clue.
How the clue works
The possible basis of fad diet points to the grapefruit diet. Take "Fig", "pear" and "turn" cut short ("almost" trims the last letter to give TUR), then the indicator "out" tells you to rearrange all those letters — FIG PEAR TUR — to spell GRAPEFRUIT.