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I may be very off on many scientific details here, but I'm always all ears.

As far as I understand, any food that is eaten goes to the stomach, gets broken down even further into smaller food molecules, and after a period goes through the intestines where nutrients are absorbed out of this chyme.

Let's say I eat food A sometime, and it's gone down and is now sitting in my stomach, waiting for the stomach to start breaking it down. After a while, I eat food B.

When digestion occurs, is it possible that the stomach only starts breaking down food A's material first before it gets to food B? Is it possible that food B's output goes into the duodenum before food A's output?

Please help break any of this down if it's obvious I've been living in a cave. Thanks!

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  • $\begingroup$ I'm curious, do you have a reason to believe the stomach would act in such a selective manner, when it is using muscles to churn the material around? (also, did you get your question backwards? Did you intend to ask " Is it possible that food B's output goes into the duodenum before food A's output?") $\endgroup$
    – Cort Ammon
    Feb 4, 2016 at 1:09
  • $\begingroup$ @CortAmmon I have had no strong reason to chase down this answer, but I was really curious because this could, if answered positively, in a way, help me figure out potentially which meal was causing any current discomfort inside. $\endgroup$
    – andeart
    Feb 4, 2016 at 1:13
  • $\begingroup$ Ahh, so you are specifically referring to the case where the meals are several hours apart? Since the stomach usually digests food in anywhere from 40 minutes to a few hours, the amount of time between A and B would matter. $\endgroup$
    – Cort Ammon
    Feb 4, 2016 at 1:15
  • $\begingroup$ You would have to eat each meal independently and wait a ridiculous number of hours to figure out where your discomfort is coming from. Mean time from mouth to excretion is along the order of 40 hours, and so the time trial would determine something like is the discomfort originating in the stomach, the colon? An important fact to note is that food in the stomach is pulverized to chyme so if you eat meals close to one another, it can confound things. $\endgroup$
    – CKM
    Feb 4, 2016 at 1:17
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    $\begingroup$ It all depends on the delay between the consumption of food-A and food-B. It is all a continuous process (without any thresholding) and there is certainly a likelihood that there would be some minimum delay below which you get a well mixed chyme of both foods. Also, depending on the nature and composition of food these kinetics may vary. $\endgroup$
    – WYSIWYG
    Feb 4, 2016 at 4:24

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In general, food is not kept in any particular sequential order. The stomach has a lot of smooth muscle which churns the food, very rapidly erasing any "order" to the food. Beyond that, the stomach digests "the food in the stomach," in parallel. Whatever is in it, it digests.

Now, in general, food eaten earlier will digest into chyme (the digested slurry which enters the intestines) sooner, but that's a very general pattern and doesn't account for any differences in how long it takes to digest various types of foods.

I don't have any sources to back this next claim up, but I do believe that if you were to chew some steak poorly, and then follow it up by more steak chewed properly, the later steak would actually digest first because it would take less mechanical processing in the stomach to get the digestive enzymes to where they need to be to work.

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  • $\begingroup$ Thanks for the response. When the chyme rests in your stomach, before it moves towards the intestines, how does the stomach treat new food that has just reached it? $\endgroup$
    – andeart
    Feb 4, 2016 at 1:43
  • $\begingroup$ think of it as a large ziplock bag. Food goes in, joins whatever mix of chyme and bollus (chewed food) happened to be in the bag at the time. Give the bag a few squeezes to mix things up. It's really more of a continuous process than a batch process. Most of the exciting stuff is happening at the molecular level, so it doesn't really care about what the mix looks like at the macroscopic level. It doesn't care if its breaking down the last few protiens of the last meal, or fresh protiens from a newly chewed steak. $\endgroup$
    – Cort Ammon
    Feb 4, 2016 at 2:02
  • $\begingroup$ Any description of digestion I've read mentions it, so if you feel bad sans source, that's place to start looking. That said, you really, truly ought not need to cite every blasted well-known and fundamental fact. If someone really needs to get more input on the point, they can always post that specific question on Stack Exchange, too. $\endgroup$
    – The Nate
    Feb 4, 2016 at 2:19

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