For me, someone with intestinal fortitude is someone who can eat almost anything without getting sick or throwing up. You might use the phrase to describe a traveller who manages to eat gruesome, ultra-spicy, or unhygienic things without ill effect. I wouldn't use the phrase to refer to someone who's gutsy or resilient (though a person could also coincidentally be these things).
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FuturistI wouldn't use the phrase to refer to someone who's gutsy or resilient (though a person could also coincidentally be these things).I take the opposite view on this. For me, the meaning is always figurative and has nothing to do with the physical functioning of one's innards.
Mr WordyI take the opposite view on this. For me, the meaning is always figurative and has nothing to do with the physical functioning of one's innards.I should really have done some googling before posting my answer. The sense that victo and Mr. Wordy refer to is indeed in widespread use.