# Question about food and digestion.

**URL:** <https://boards.straightdope.com/t/question-about-food-and-digestion/378952>\
**Category:** Factual Questions\
**Created:** [November 3, 2006, 9:01am UTC](https://boards.straightdope.com/t/question-about-food-and-digestion/378952 "2006-11-03T09:01:37Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![copperwindow](https://avatars.discourse-cdn.com/v4/letter/c/4af34b/32.png) [@copperwindow](https://boards.straightdope.com/u/copperwindow)\
**Post date:** [November 3, 2006, 9:01am UTC](https://boards.straightdope.com/t/question-about-food-and-digestion/378952/1 "2006-11-03T09:01:37Z")

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What makes a purple plum purple?

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**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\
**Post date:** [November 3, 2006, 9:49am UTC](https://boards.straightdope.com/t/question-about-food-and-digestion/378952/2 "2006-11-03T09:49:25Z")

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[Anthocyanins](http://en.wikipedia.org/wiki/Anthocyanin).

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**Author:** ![copperwindow](https://avatars.discourse-cdn.com/v4/letter/c/4af34b/32.png) [@copperwindow](https://boards.straightdope.com/u/copperwindow)\
**Post date:** [November 10, 2006, 10:10pm UTC](https://boards.straightdope.com/t/question-about-food-and-digestion/378952/3 "2006-11-10T22:10:47Z")

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After I ingest the plum, what happens to the anthocyanins? My urine and poop isn’t purple. Where does the “purpleness” go?

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**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\
**Post date:** [November 10, 2006, 11:04pm UTC](https://boards.straightdope.com/t/question-about-food-and-digestion/378952/4 "2006-11-10T23:04:06Z")

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In general digestion means breaking larger molecules down to smaller ones that can be absorbed through the intestinal walls. I don’t know the chemistry of Anthocyanins in particular, but most probably they are broken down into pieces that are no longer purple-colored.

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**Author:** ![chorpler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chorpler/32/2888_2.png) [@chorpler](https://boards.straightdope.com/u/chorpler)\
**Post date:** [November 13, 2006, 11:27pm UTC](https://boards.straightdope.com/t/question-about-food-and-digestion/378952/5 "2006-11-13T23:27:04Z")

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[QUOTE=copperwindow]  
After I ingest the plum, what happens to the anthocyanins? My urine and poop isn’t purple. Where does the “purpleness” go?  
[/QUOTE]

They get digested and metabolized.

This doesn’t happen with some colorings, though, especially with some of the colorings they use in food nowadays, or that you can buy in the store as “food coloring” in little bottles. I remember being shocked as a kid after I made a blueberry smoothie that called for blue food coloring, and my poop turned dark blue-green.

… oh, and the above is only valid for feces, since some stuff can pass straight through your body that way. Urine is filtered from your blood and therefore it doesn’t turn colors depending on what you eat – only depending on how much waste material is dumped into it. (There are substances that dye your urine, but they’re not common. The drug Pyridium, for instance, is a dye that turns your urine dark orange, or even dark bloodlike red if you take more than one pill, that supposedly anesthetizes your urethra; they often prescribe it for kidney stones, post-catheterization urethra hurtiness, and other problems where your urethra is … um … hurty.)