Guts: FIFO?
July 30, 2012 8:04 PM   Subscribe

Intestinal systems: FIFO?

First In–First Out: Is that how guts work? Or is there some mechanism that promotes some material forward while holding other stuff back?
posted by five fresh fish to Grab Bag (6 answers total) 2 users marked this as a favorite
No. My med school boyfriend tells me that your stomach is a mixing bag and a separator at the same time.

A meal sits in your stomach and the stomach vibrates To sort things.
Fats go first and he last thing s that exit are fibrous, like veggies.

He says the fiber kind of acts like a pipe brush.

(Then things might collect again and mix in the large intestine. He's not currently studying GI, having just finished a psychiatry rotation.)
posted by tulip-socks at 8:20 PM on July 30, 2012 [1 favorite]

There isn't any resorting mechanism, but things can get very mixed up in the stomach. The fact that you feel hungry doesn't mean your stomach is empty.
posted by Chocolate Pickle at 8:20 PM on July 30, 2012

The stomach is a mixer to be sure. A buddy of mine once ate a giant burrito, waited over an hour, then took a chugging bet involving a bottle of pancake syrup... He ended up booting the burrito debris first FOLLOWED by the syrup. I assumed it was a density issue... it looked like black death... seriously kids, it is not as easy as they make it look in Super Troopers.
posted by milqman at 9:02 PM on July 30, 2012

This reddit thread provides a good answer. In summary:

"Your GI large and small intestines are pretty much first in/first out. After you eat, your stomach will churn up your meal to mix it with the acid in the stomach** and break it down into small enough pieces to pass through your pyloric sphincter,** and depending on it's chemical makeup will dole it out a little bit at a time into the small intestine. After about 4 or 5 hours, the entire meal will have left the stomach, so unless you eat your meals within a couple hours of each other they won't mix."

But keep in mind that:
"Substances do not move uniformly through the digestive system.
Materials do not leave segments of the digestive tube in the same order as they arrive.
In other words, a meal is typically a mixture of chemically and physically diverse materials, and some substances in this mixture show accelerated transit while others are retarded in their flow downstream.
posted by Adamsmasher at 9:07 PM on July 30, 2012

On a bite-by-bite basis, no, it's not FIFO. But on a meal-by-meal basis, it is for the most part.

Everything you eat over the course of an hour or so is getting mixed up in your stomach, then gradually squirted into your small intestine in little bits at a time. So the bites of roast beef and mashed potatoes and peas from dinner are all pretty well combined by the time they make it to the intestine. Assuming you don't eat another meal for several hours, your stomach is mostly empty by the time pancakes and scrambled eggs show up, so they get mixed together with each other, but not with the previous meal. Last night's dinner is now making its way through the small intestine, where it continues to get mixed up and separated and recombined with itself. The small intestine is over 20 feet long, so it takes a while to make its way through, but it is already partway through the tube by the time breakfast gets added behind it. Certainly it's possible that some bits of breakfast get mixed in with some bits of last night's dinner while traveling through the intestine, but there is no sorting of nutrients or alternate paths for anything to take. The food basically gets in line and gets pushed out the other end after a day or two.
posted by vytae at 8:33 AM on July 31, 2012

Thank y'all.
posted by five fresh fish at 10:39 PM on July 31, 2012

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