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.