Physics, Poop, and Questionable Medicine

Normally I stay mostly on the physics beat, trying to mostly stay out of the controversy arena except occasionally when my lunatic reactionary politics crops up in something like my Social Security piece a while back. But all things considered I much prefer to a nice, collegial, uncontroversial discussion about eigenfunctions of the Dirichlet problem than charging in with guns blazing to the nearest eruption of sloppy thinking.

Nonetheless there are occasionally times it's just not possible to look away. Another ScienceBlogger brought up a piece on the Huffington Post by a well-meaning lady named Kim Evans. She says a lot of things, some sensible, some totally bonkers. I suspect a lot of unknowing readers of her piece may be lead astray because of lack of basic physics/math understanding. When people (for instance, my students) ask "What good is physics to the non-physicist?", well, one reason is that they develop some intuition for how the world works. Density, for instance.

Density? Yep, understanding a concept so simple can save you from a lot of trouble. Let's listen to Ms. Evans:

Cleansing involves changing your internal environment and specifically, removing a bunch of the stored waste that most people have trapped in their bodies. Most estimates are that the average person has ten or more pounds of stored waste just in their colon, and I'd argue far more throughout their body. In any case, many people have found that disease disappears when this waste is gone, and that when the body is clean it's much more difficult for new problems, like viruses, to take hold in the first place. And it's my understanding that many people who took regular enemas instead of vaccines during the 1918 pandemic made it out on the other side as well.

"Cleansing" in this case is what it sounds like. I don't know and am frankly a little scared to find out what her particular method involves, but one presumes it is not so far from the standard way to clean out bodily orifices. That's not the point. The point is TEN POUNDS OF WASTE ARE YOU SERIOUS?! Gah! Surely that's not good for me, I'd better get rid of it ASAP...

If there's really ten pounds of waste trapped in there, of course. Density can help us figure out if that's plausible or if Ms. Evans is full of sh..., well, you know. Density is mass per volume. It's an intensive property of a substance, and knowing two of the three of mass/volume/density lets us figure out the other. I have no idea what the density of "waste" is, but we can give a very close estimate. Not to put too fine a point on it, sometimes poop floats and sometimes it sinks. This means its density is roughly that of water, varying a little bit depending on what we eat and drink and whatever other mysterious digestive processes happen to be ongoing in our bodies at the moment. Therefore if we say poop has a density equal to that of water, we know each cubic centimeter has a mass of 1 gram, give or take a few percent.

We have mass* ("ten pounds or more") and density. Volume is mass divided by density. So let's take ten pounds and divide it by 1 gram per cubic centimeter.

Four and a half liters. That's 1.2 gallons. Minimum, depending on how you construe her "or more". I don't know if you really want to picture what that volume of waste would be like in a human body, much less where it would fit, but it's clearly not possible. If you filled the entire volume of the large intestine you'd be hard pressed to reach this. There have been cases of bowel disease or obstruction where waste has accumulated (urban legends about John Wayne and Elvis occasionally surface in this context), but it's far from normal, far from 10 or more pounds, and far from anything that can be fixed by a bag and a hose. To say that an average person has two two-liter bottles and a 20 oz bottle full of stationary poop loitering in their colon is preposterous on its face. And that's before considering the fact that surgeons poke around in thousands of people every day and don't see anything within orders of magnitude of Evans' claim.

Take care of yourself, eat right, exercise. By all means get colon screenings for cancer as you get older. But please don't treat yourself like a sink in need of Drano.

* Formally we have the standard technical point about the distinction between mass and weight in English units, but there's no need to split hairs. For our purposes a pound is a unit of mass equal to about 0.45 kilograms.

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Matt, I have nothing scientific to contribute to this topic, but I want to offer my opinion on the subject matter... This is utter CRAP, Mr. Springer...unadulterated CRAP!

according to your scibling Dr. Pal in a recent post on turd quackery, poo is supposed to sink. That also matches my experience. The density of poo may therefore be, on average, a bit higher than that of water.

C'mon, some poor grad student somewhere must've figured this one out, no?

You'll be happy to know that this blog post comes up on the first page when I googled "density of poop".

i used google-fu to find:

small intestine 6 m long, 2.5 cm wide.
large intestine 1.5 m long, 6.3 cm wide.

volume of small intestine = 600 cm * (1.25 cm)^2* pi= 2900 cc
volume of large intestine = 150 cm * (3.15 cm)^2*pi = 4700 cc.

So the volume of the small intestine is almost 3 liters, and the large intestine almost 5 liter.

so, you *could* fill up the large intestine with 10 pounds of poop, but not much more, and i wouldn't make any bets on how any newly digested food gets through a filled up large intestine.

it is so easy to debunk many of these dubious claims. yet people *still* believe in them.

a) I agree that the density is generally higher than water when things are working right and the water content isn't too high.

b) ", far from 10 or more pounds"

I dunno, have you ever seen the megacolon at the Mutter Museum in Philadelphia? That thing's big enough to pass a volleyball through. I bet he had more than 10 pounds in there when he died. Then again, he died.

"So the volume of the small intestine is almost 3 liters, and the large intestine almost 5 liter."

That's probably true if you've pulled them out and used them as sausage casings, but in their normal arrangement I don't think they're suited to being fully distended along the entire length. I suspect they depend on most of the length being compressed, except for the parts that are busy passing some feces.

Nice analysis, but I doubt that Ms Evans (or for that matter anyone at Huffpo) would really care that their theories go against the laws of physics. After all, their resident "doctor" has a doctorate of homeopathy who believes that water molecules have memory.

Having had a colonoscopy and done the day before "cleansing" I can guarantee you there wasn't 10 lbs of poop. Is that TMI?


By CHRIS HERTLEIN (not verified) on 30 Apr 2009 #permalink

Maybe Ms. Evans drew her conclusions from studying blivets.
For those of you who don't know--a blivet is a five pound bag filled with ten pounds of --you can finishit yourself.

Well shit...

"don't see anything within orders of magnitude of Evans' claim."

Two orders of magnitude is a factor of 100. Surely .1 lb is within reason

Doing some physical measurements on the exterior of my abdomen, estimating wall thickness with some judicious proding and pinching, and using a rough estimate gleaned from cleaning fish and rabbits of .5 for ratio of organs to intestines therein, I estimate I would likely have a total intestinal volume of the order of 5l total. I know I can drink a full litre of beer with some noticeable distension consistent with my estimates. Thus I would estimate the ten pound estimate for "waste" would imply things were indeed desperately backed up back to the tonsiles...

The part I note in the quoted passage - "and I'd argue far more throughout their body." Now where this "more" than ten pounds is stored I do not dare guess beyond possibly imagining Ms Evans with a very swelled and full head.....

It certainly gives a new insight on the expression "full of shit"

If this had come up before my colonoscopy, I could have done a before and after weighing, but the simple Fermi-style calculations of others seem reasonable about the volume and weight involved.

Observation 1: The volume of your abdomen consists mostly of your intestines and your liver. Is there room for a gallon milk jug in there? For most people, yes. For some, there is room for a gallon jug above their belt.

Observation 2: The retention time for your digestive system is close to three days. (Fairly obvious after a colonoscopy.) How much does three days of crap weigh? Hopefully not 10 pounds, but much of what is in your stomach and small intestine is liquid that is eliminated through your kidneys.

This last point means that a better measure of what most people think of as "waste" would be the mass of dry solids, not the total mass in the intestines. That is unlikely to be as large as 10 pounds for most people.

By CCPhysicist (not verified) on 02 May 2009 #permalink

Good point CC. There could be several pounds total from the stomach to the rectum at any one time. The key point is that it's moving. Presumably Ms. Evans is fine with that. But that there's waste stuck in there that's 10 pounds over and above the normal moving material is just not possible in a person not experiencing a medical emergency.

Advertising suggests that it is not moving in everyone in the US population. Maybe you young folks don't watch programs where they run those ads. ;-)

There is also a non-zero chance that some part of it is not moving - trapped along the sides - as a result of either a medical condition or the contents of the typical US diet. But I agree that a person would have to be severely obese for the dry weight of that stationary amount to approach 10 pounds.

I'm not about to go back and read the original article, but it probably conflates a true statement (total mass of waste in your body) with an untrue one (total mass that is not moving) to create a false impression and an effective salse pitch. This is common in both commercial and political advertising. Just compare the front text of a drug add with the page and a half of fine print on the next page if you want an example.

By CCPhysicist (not verified) on 03 May 2009 #permalink

Indeed. and nicely done. What about the compressibility of poop? unlike water poop can be compacted. That corpse-like Dr Gunter von Haagens (sp?) has some slices of a woman with a massively obstructed colon - as seen on Jamie Olivers "eat to save your life". It was pretty clear she hadnt shat right for years.

which really means that an amazingly poor diet can lead to chronic bowel obstruction. 10 pounds is both a silly unit and a likely exaggeration, but not outrageously so - except of course when referring to the "average" person, as such people are clearly extreme examples.

Lies, damn lies and innumerate morons :)

By terry given (not verified) on 03 May 2009 #permalink

Let's be generous now: the poor woman was merely reifying one of the guiding metaphors of our culture: 10 lbs. of shit in a 5 lb. bag. She just got a little dramatic -- happens all the time on CNN, Fox News, and MSNBC, among other places. Let's also remember that this is the Huffington Post style -- it's a site modeled largely after those admirable British tabloids, which contain 98% shrill gossip and cheesecake porn, 2% being the occasional gem (hey, Dean Baker and Jared Bernstein write there, a couple of the most lucid economic voices amid the current global unpleasantness). And, however you wish to abhor the fact of it, HuffPo succeeds, in terms of traffic, advertising, and money. The guiding principle: we will not care what AIG or Citibank is doing unless we also can see what Michelle is wearing.

Some very large tumors, such as ovarian cancers, uterine fibroids or liposarcomas are found in the retropertioneal space. Basically, in the potential space where the kidneys lurk. Those tumors can get very, very, large, 25 Kg or so. Now, they are slow growing, and hard to detect. But when they get that big, most people report their pants don't fit.

By William the Coroner (not verified) on 08 May 2009 #permalink

There is still something to be said for the traditional units still used in the U.S. these days. Remember, "a pint's a pound the world around", so ten pounds of water is ten pints, or five quarts or a gallon and a quart[er]. Isn't that much easier than that nasty, new fangled metric system?

I love poop discussions, my cat is named poopie!