Friday Weird Science: Fatty Feces or Gassy Guano?

May 03 2013 Published by under Friday Weird Science

Does your poop float? Does it sink? Do you have floaters and sinkers depending on the day?

Maybe you're one of those people that never looks to see.

Nah, don't lie. You look.

So if you have looked, surely you've wondered...what makes poop FLOAT? I seem to recall asking my mother this once as a kid and she told me it was fiber and that fiber floats. Since I have now found out that, chemically, that's a dirty lie (she didn't know, so it wasn't intentional, and she always has promoted a high fiber diet), I continued to wonder...why does some poop float while other poop sinks?

The answer, my friend, is blowing in the wind. As it were.

bristol stool chart
(Source. You know that you will now be looking at and rating all your poop. It's unavoidable.)

Levitt and Duane. "Floating Stools - Flautus vs Fat" New England Journal of Medicine, 1973.

The possibilities for floating poop are pretty limited. If poop floats, it must have something in it that is less dense than water, right? And what do we have in us to poop out that's less dense than water?

Well, we have FAT. And until this paper came out, it was widely assumed that people who pooped floaties had fatty feces. This is actually a medical condition called steatorrhea (word of the day! Work it into a sentence with your coworkers. Go on, I dare you). It's not harmful really, but lots of fat in your turds can indicate things like a lack of acids in your bile. So it seemed odd to these authors that, even though a lack of acid in the bile is pretty rare...about 10-15% of the population regularly had floaties (I would really love to know where they did the survey for this number "Hi, is this a good time to call? We are conducting a brief survey of your s**t, it should only take a few minutes of your time...").

So is it really fat causing all the floating? Well, clearly you need to do science. So the authors of this study got 9 people whose poop floated, 24 whose poop sank, and 6 people who definitely did have steatorrhea. They pooped.

Then the intrepid investigators (and they must have been intrepid for this one), had to TEST the poop to see if it REALLY floated, so they took a piece of each person's poop and put it in some water and checked (you'd think they could just have checked the toilet bowl, but no). Then, they assessed the density of the dung, with classically scientific methods.

floating poo1
(From the methods. The cheese slicer is the scientific term.)

The piece of poo was assessed for density, and the rest was analyzed for fat content.

And then they analyzed for GAS. And in the methods, the real reason for the study came out.

floating poo2

I love that. The true measure of a scientist. "Hey, my poop floats! That's weird, I wonder why? Well. I DO fart a lot..."

And it turns out, the investigator had it right. Poop that floats isn't's GASSY.
(Figure 1 from the paper)

Here you can see the specific gravity (a measure of density) of the poo from the various groups. The floaters are on the left, the sinkers are in the middle, and the fatty feces people are on the right. You can see that the density of the floaters and the fatties is much lower than that of the sinkers...until you remove all the GAS. When you remove the gas, the floaters achieve a density that matches the sinkers, while the fatties are still low. So we know that for people with steatorrhea, the fat is what changes their density, but for the 10-15% of the healthy population with floaters? It's all about gas.

And so, in a way, my mom was actually right. Fiber probably CAN make for floaters, especially if the fiber produces more gas. So the next time your poop floats, or sinks, take comfort. It's not fatty feces, it's just some gassy guano.

18 responses so far

  • Hermitage says:

    Well now I feel better. Dr. Oz via Oprah brainwashed me into believing that floaters meant that I was full of fatty mcfaterson and was going to die of heart disease at a young age.

    • scicurious says:

      SERIOUSLY?! This paper is from the 1970s!!! Shameful on his part.

      • Hermitage says:

        And this chart can't be right because Dr. Oz said my poop should be S-shaped or I else I have an unhealthy gastrointestinal system.


  • AMW says:

    I love that they outed the author with the excessive flatulence. I'm sure everyone within a certain radius of the lab already knew, but you gotta figure his national colleagues were like, "Note to self: don't sit next to Bill Duane at the next ACG Meeting."

  • ryandake says:

    sci, you are on a poop bender lately. since that's the case, how about telling us how one ends up with all those different types? any science done on which variety is most aesthetically pleasing?

    • Brian says:

      This could be a job for citizen science.
      I believe:
      #1 comes along for me after eating bagels.
      #4 on the chart can be achieved by beer the night before a sitting.
      #6 after a chinese buffet.
      #7 is usually viral or bacteria infection.

  • Tom Hennessy says:

    Floating feces is used to diagnose some type of malabsorption disease in which the feces smell bad , real bad , peels paint. One might wonder then , is it excess methane which causes the paint to peel ?

  • This post was a right gas. I didn't realise there were actually papers on this; when I saw the title I assumed you were full of it. (Er... I'll get me coat)

  • namnezia says:

    I've been trying to convince my wife to let me put up a framed Bristol Stool Chart in our bathroom, but somehow she keep refusing. I don't understand why. I keep telling her it's like cloudspotting.

  • [...] sinking feeling. Discerning the hows, whys and wherefores of poop that floats (or not). Yes, [...]

  • Timfin says:

    Lovely Article on a smelly subject! I Believe Mom, (They're always right.) had it right. Forgive me for not citing sources as I gotta get to work, but I believe fiber has been shown to reduce cholesterol by absorbing fat and carrying it out the pipe. This additional fat, albeit along with methane CH4, keeps the ships afloat.
    GOD Bless You

  • Schnzrpunk says:

    A most enlightening read! As a lactation consultant, I am a big fan of poo charts; it's amazing how much a soiled nappy (diaper) can tell us about a baby's feeding, health and gut maturation! In our home (hidden behind the toilet door, in case company think we are wierd!) we have a range of poo charts, including the Boston! But the issue of "unflushables" has been a source of my eldest (autistic) son's latest passion...
    I had wondered, based on my own observation (a practising sociologist in pre maternal life), whether days of v high green vegetable intake, compared to heavier protein days, compared to high fibre complex carbs had any impact. (I am coeliac, with low fructose and lactose toleration, so I have an extremely limited and low processed food diet).

    Turns out the protein heavy days lead more closely to Boston type 2 sinkers, carb days are type 3 bostons and can sink or float, but flush easily. But (drum roll) the days where my vegetable intake is v high give Boston 4-5, and often lead to the fabulous unflushables. Given my fructose issue, the veggies of most heavy intake are carrot, baby spinach, cauliflower, tomato, sweet potato, pumpkin, taro, aubergine, Asian greens, bitter greens, peas and fresh green beans.

    OMG! PhD in liberal arts, and I'm taken a Sheldon cooper view of toiletting! What went wrong?

  • Tim Lundeen says:

    Do you have a full copy of the paper? I'm curious whether the floating stools had higher butyrate content, and whether they checked that.

    The Keep Hope Alive site says "At that time I had no idea why the buoyancy of the stools was linked to the fate of the CD4’s. Now as this decade and century comes to a close, we finally understand the connection between colonic pH, CD4’s and the viral load. It is directly linked to the presence or absence of acid producing friendly intestinal flora in the colon. When the stools sink the CD4’s fall and when they float, the CD4’s rise. The reason the stools float when lactic acid producing bacteria are in the colon is that the friendly flora produce short chain fatty acids that make the stool lighter than water."

    So, it looks like their explanation for why floating stools happen isn't correct, but they still seem to be associated with good health. So I'm curious to understand more about this...

    • T. H. says:

      I have been taking a probiotic (Probiotic-3 by AOR) for several weeks that has soil-based strains intended to produce butyric acid in the intestine. I have also been taking potato starch to feed these bacteria. Since I've been doing this, my poop almost always floats. Before starting the probiotic, I regularly stopped up the toilet with large, heavy stools. You might be on to something.

  • Kevin Phelps says:

    who's checking poop for that poop checkers daughter while that poop checkers are out checking poop?!

  • Michelle says:

    I have a lot of gas but my... Excretions always sink. Also, i get extremely gassy right around lunch time, and it doesn't go away until I get home (4-5 pm) where I can comfortably pass gas. My stomach obviously hurts very bad from holding everything in. I can never poop everyday, usually I go once or twice a week, no matter how much fiber/fruits/vegetables I eat. This has only started recently, maybe since the summer of last year. I can't keep going like this, I get number 6 on the chart about every two weeks or so for some reason. I've tried different foods, not eating for the whole day, etc but nothing changes.

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