There Will Be Blood... And Poop

February 29, 2008 4:00 PM

Was my poop weird because I donated blood? SFW but contains qualitative poop analysis. Really.

A couple of days ago, a buddy and I were recently discussing that human poop contains a large proportion of dead red blood cells, which are apparently responsible for its characteristic dark brown hue and idiomatic reek. The following day I donated one unit of whole blood. Since the blood content of poop was fresh in my mind, I observed my subsequent bowel movements with interest.

The day following my donation, I pooped at my usual time (I am a very diurnal pooper) and it was in fact much lighter in color than usual (sort of beige) and had less poopy smell than usual. The second day (today) I had a more familiar poop — bittersweet chocolate colored and smelly. I actually ate almost exactly the same foods on both days. FWIW, I also have a very fast metabolism. I eat like a pig and barely weigh enough to donate blood.

Was my poop actually lighter and pleasanter due to a sudden erythrocyte deficit?

posted by mindsound to health & fitness (9 comments total)

IANAD. Bilirubin is the stuff that makes your poop brown. I can't quite make sense of this wikipedia article about it, but it seems more like bilirubin levels are conencted to what your liver is up to rather than your net volume of blood.
posted by jessamyn at 4:19 PM on February 29, 2008

Well, you're half right. As jessamyn suggests, Bilirubin is one of the substances that makes your feces brown. It comes from the breakdown of hemoglobin, which, in turn, comes from the breakdown of old red blood cells.

I'm not a doctor, and it's been a while since I took phys or pathophys, but it would make sense that the rate of red blood cell breakdown would slow after significant blood loss. I couldn't give you the specific feedback mechanism responsible, but perhaps an MD can help out with this one.

If I were on mythbusters, I'd label this one "plausible".
posted by chrisamiller at 4:46 PM on February 29, 2008 [1 favorite has favorites]

Jessamyn is looking for stercobilin, which makes poop brown. Biliverdin comes from "dead" red blood cells, which then gets converted to bilirubin. Bilirubin is excreted by the liver as bile. Some of the bilirubin gets converted by bacteria to urobilinogen, some of which gets reabsorbed and peed out (making your pee yellow). The rest goes through more conversions until voila, stercobilin.

No idea about your hypothesis. How about... maybe?
posted by gramcracker at 5:44 PM on February 29, 2008

No. Breakdown of RBCs is somewhat obligatory. Loss of blood would reduce the total available for turnover, but not that much. It also wouldn't come back in one day. It's worth keeping in mind that you aren't losing that much blood in a donation.
posted by a robot made out of meat at 6:39 PM on February 29, 2008

When I'm very sick and eat very little for a few days, my first solid crap once I get better is, for lack of a better term, "blonde". I've always figured that my body wasn't culling red blood cells. I'll be damned.
posted by notsnot at 7:40 PM on February 29, 2008

It also wouldn't come back in one day.

I'm not necessarily arguing with your conclusion (because I'm still unsure), but I think one day is plenty of time. The average transit time from mouth to rectum is 24-48 hours. Assuming the poster is on the short end of that scale, food that's up near the bile ducts could certainly be passed the next day.
posted by chrisamiller at 11:19 PM on February 29, 2008

Keep giving blood and analyze your poop. Pop by this thread every 6 weeks to post a poop update. It does sound plausible.
posted by happyturtle at 4:32 AM on March 1, 2008 [2 favorites has favorites]

My vote is unlikely but plausible perhaps. I'm not a 100% sure. When you donate blood you're losing about 10% (generally less) of your blood volume, which means you're also losing about 10% of the red blood cells that would probably be turning over soon. If this translated to 10% less stercobilin I'd say that shouldn't cause a major change in color. However, there is the possibility that a larger fraction of the products of bile are then reabsorbed in the distal small bowel as a possible physiological response to impending anemia and the need to produce more heme. Homeostasis might benefit from increased reabsorption as some of the materials in the bile are helpful in the production of new blood cells. As a result, perhaps it would lead to lighter stools.

Of course this is all conjecture, and I have to say that in my experience looking squarely at the stool of people who develop acute anemias far more severe than what you're talking about quite frequently (love my job), I've never seen a major change in color.
posted by drpynchon at 11:48 AM on March 1, 2008

happyturtle: you can donate whole blood every 8 weeks, not six.

mindsound: I don't know the answer, but please keep donating! If you qualify*, you could try donating a double-unit of red blood cells (it's an apheresis procedure, similar to donating platelets). Poop results might help support/negate your hypothesis

*You generally have to be a certain weight/height to donate double-red. Also, depending on your blood type, they may or may not have a higher demand for your red cells If you're an O or B, they'll probably want them, if you're an A, stick with whole blood or maybe do platelets.
posted by radioamy at 10:05 AM on March 2, 2008