It is from this article. Here is the context:
Whether any one person can or should include fruit in their diet depends on a lot of things.
What I cannot get is the use of the word one there. What did the author use it for?
asked Oct 30 '18 at 9:55
one person is being used there as a synonym for individual.
Whether any individual can or should include fruit in their diet depends on a lot of things.
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There can be shades of difference, yes. Individual asserts a uniqueness that person does not, hence "any one person". And some speakers will even feel that individual does not assert uniqueness strongly enough and thus say any unique individual, which other speakers would consider pleonasm. – Tᴚoɯɐuo Oct 30 '18 at 12:25
I believe the author tries to emphasize this fact that each person, individually has to conform to special rules. And each case should be investigated according to special circumstances because he or she might have dietary restrictions, food allergies and other factors and influences that are not true about the others.
I personally think the "one" can be removed, but it is there to emphasize.
