Why isn’t beetroot dye broken down by digestion?

29 November 2009

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Question

Why isn’t beetroot dye broken down by digestion?

Answer

Chris - Well, in some people it is, but in some people it isn't.

The chemical that's in beetroot that makes them red and makes some people wee red and also pass red faeces, which is what can happen if you eat a lot of beetroot, is a chemical called betacyanin.

It's actually an anti-oxidant that the beetroot makes and it can be used a colour-change indicator too, but it doesn't necessarily break down in the intestines of all people.

The things that seem to make it breakdown more are acidity, so if you have very strong stomach acid then it breaks down more. If you have weaker stomach acid, then more can get through into the small intestine, and there, pancreatic juice is alkaline. So that can encourage it to pass through into the colon, which is actually where it's absorbed.

People have done experiments on patients who have had things called ileostomies, which is where you take the ileum, the terminal bowel, and you bring it to the surface of the skin. And you take the contents away into a bag, for example. If you feed these patients with the betacyanins in beetroot they don't ever get beeturia, in other words, the red dye getting into their urine. That shows that the absorption must take place in the large intestine.

The other things that seem to affect the absorption is a chemical called oxalate, oxalic acid, which you get from rhubarb and rhubarb leaves. That actually gets broken down by bacteria in the small intestine and in the large bowel. So it's possible that there's a combined effect whereby some people have a certain genetic makeup that makes them break this stuff down more than others because they have more acidity.

It's also possible that they have certain bacteria living in the intestine that breaks this stuff down more than others, and so that affects whether or not you see it appearing in the bloodstream.But in people who do get beeturia, what seems to happen is that the pigment comes through the wall of the bowel, doesn't get broken down, goes around in the bloodstream, and then it gets filtered out by the kidneys and goes into urine, and makes urine go red. But what's really interesting is that on its way to the kidneys, of course, it has to go through the blood.

I was rooting around on the Internet and I found this wonderful paper. It was published in the Christmas BMJ 2005 by two doctors, Julia Handysides and Stuart Handysides, who work in Essex... I'll read you this because it's hilarious:

"One Sunday evening in 2004, our 11-year old son went to bed after various delaying tactics, arguments about friends staying up later, forgetting to brush his teeth, forgetting to come down for a drink of water, and so on. But shortly afterwards, the dining door room opens, and in he comes, cupping a bleeding nose in one hand and gripping the bridge of his nose with the other. We led him to the kitchen sink and helped him to clean up and stem the bleeding, but oddly, the blood on his hands would not wash off. And it also looked brighter than usual. The poor child was interrogated. Is this some kind of ruse or lark to stay up later? The bleeding stopped, his hands, although stained pink, were now clean and dry. Upstairs, we found crimson stains on the bathroom carpet which proved impossible to shift and remain there over one year later. Our garden's harvest of beetroot was very good in 2004, and we had eaten some the day before the nosebleed. It dawned on us that on its way to staining urine, the pigment in beetroot might also stain blood as well."

So, that means potentially, all of your internal organs are getting stained bright red by beetroot, and if you bleed, the stuff can come out and stain your skin. I mean, that's just amazing!

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