Digestion and the end result.

January 27, 2009 11:43 AM

This is a question about digestion and the end result. This is purely a matter of abstract curiosity. I promise not to provide too much information.

OK . . . here goes:

At what point in the digestive tract does food start to resemble feces?

Is it in the large intestine? The colon? Does this vary for different types of food? Would yogurt, for example, convert to feces at a different point in the digestive tract than, say, a big piece of steak?

Does this vary for different people? Or is this point pretty universal?

Thanks for your time.

posted by jason's_planet to health & fitness (11 answers total)

I'll leave the full answer to the anatomists, but one can clearly see that food stops resembling food quite quickly by examining one's vomit.
posted by Pollomacho at 11:52 AM on January 27, 2009

Yeah, but Pollomacho, vomit doesn't look like feces.
posted by amro at 11:54 AM on January 27, 2009

Granted, amro, however, one can clearly see that the breakdown begins very quickly and vomit is far closer to feces than a pork chop.
posted by Pollomacho at 12:06 PM on January 27, 2009

I would advice the poster to do a bunch of image searches related to Colostomy, Colostomy bags and other related material.

The bile should give it a nice shitty color already in the small intestine so if it's looks you're after I'd say that its pretty early in the process.
posted by uandt at 12:22 PM on January 27, 2009

Much of the color and odor is a result of the mixture of the food waste with bile. This occurs in the duodenum. Of note among the components of bile is stercobilin, which gives feces its color. The mixture in the small intestine is dehydrated in the colon, resulting in the familiar texture and consistency.
posted by mr_roboto at 12:24 PM on January 27, 2009

The dark color of feces is primarily due to billirubin, a breakdown product of hemoglobin that comes from the recycling of old red blood cells in the liver. This is a component of bile, which flows from the bile duct into the beginning of the small intestine. By the end of the small intestine, most of the available nutritional value, corn excluded, has been extracted.

The large intestine is responsible for recovering water from the waste.

A lot of the smell is generated by bacterial action, which takes place throughout, but is probably greatest in the large intestine.

So, take your pick.
posted by Good Brain at 12:25 PM on January 27, 2009

One can approach this by reverse engineering. The artist Wim Delvoye built a number of Cloaca machines which convert food into poop. If you look at the machine, you can decide where the magic point where food-like becomes poo-like and start from there.

My own bias is that one of the defining characteristics of poo is that it is more solid than liquid, so the colon is key in dehydrating the chyme slurry into something that resembles poo. If color is the main indicator of poopness, then poo might start in the small intestines where bilirubin gives it it's brown color.
posted by abirae at 12:29 PM on January 27, 2009

Well, the large intestine and the colon are the same thing, first of all. The food still retains the majority of its liquid throughout the small intestine, so anything you find in there is probably going to be pretty diarrhea-looking, but I think in terms of color and, um, homogeneity it would be very poop-like. This would be particularly true in the last portion of the small intestine, the ileum, where the body is absorbing the last remainders of useful nutrients. Once the stuff gets to the large intestine, the only things really left are waste (fibers and other undigestable stuff), water, bacteria, and some minerals.
posted by vytae at 12:30 PM on January 27, 2009

I was doing a little research lately about the digestive system (I was trying to figure out how long after you eat something does it cause a fart! Still don't really know the answer... I think because different foods break down at different rates.)

Anyway I found out that your digesting food is pretty much totally liquid until the final stage in the intestines when it reaches the colon (large intestine). I guess because the liquid helps the breakdown process. Once it reaches the colon food doesn't break down any further, all the water is absorbed and it compacts into turd shape.

So that accounts for the texture and shape anyway. :)

Before that it seems to breakdown at different rates depending on the composition.
posted by thejrae at 12:32 PM on January 27, 2009

Vomit is your food along with some of the acids that help breakdown the food (thats why if you vomit too much, you lose some of the enamel on your teeth).

I'm GUESSING that feces becomes what it becomes once all the nutrients are extracted from it, and the extra waste goes in what was left of the food...so large intestine?
posted by hal_c_on at 6:08 PM on January 27, 2009

Once you are in the ileum it's pretty much shit, but depending on the individual and gut transit time it may occur sooner.
posted by docpops at 6:42 PM on January 27, 2009