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I'm thinking about giving my humanoid aliens two stomachs. If a person were to have to two bigger stomachs, would they have to eat more? If their stomachs would bigger, would they have to consume (eat a large portion of food) lots of food and would it take longer to digest?

Edit (More detailed)

I wanted to give my humanoid aliens two stomachs because I was interested in the idea. I was inspired by Stafire from Teen Titans, who has 9 stomachs. I do have a clear picture of what my aliens would look like with two stomachs but how would it work?

I'm sort of ignorant when it comes to stomachs because I don't know much about the way work. When I meant when someone were to have a bigger stomach, would they require to take in more food and would digesting be slower? Or if they had two stomachs, would the digestive process be the same or faster?

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    $\begingroup$ This is two questions: "Would they have to eat more" and "Would it take longer to digest?". Worldbuilding.SE technically discourages posing multiple questions in one post. Yours probably won't be closed since you are new here, and the questions are related, but in the future please keep that rule in mind. Also, could you perhaps provide more information about what you are looking for? Details give potential answerers a better idea of what you are looking for. For example, how much bigger are the stomachs? $\endgroup$ – The Daleks Jun 17 '20 at 16:06
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    $\begingroup$ Correct, I am new here. I'll keep both rules in mind (posting multiple questions and expanding details on question). $\endgroup$ – swilson225 Jun 17 '20 at 16:11
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    $\begingroup$ The second bit ("information, please") actually isn't a rule, it's just suggested. In any event, I hope that you stick around; if this question is any indicator, you could bring a lot of good content to the forum. $\endgroup$ – The Daleks Jun 17 '20 at 16:13
  • $\begingroup$ Okay! Don't worry because I'm not leaving (for now). $\endgroup$ – swilson225 Jun 17 '20 at 16:18
  • $\begingroup$ Starfire must have very tiny stomachs. $\endgroup$ – Willk Jun 17 '20 at 18:30
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Yes and no. You have your cause and effect backwards. They don't need to eat more because they have multiple stomachs and a long GI tract, they have multiple stomachs and a long GI tract because they need to eat a lot of food that takes a long time to digest.

Compare herbivores (especially ruminants) to omnivores to strict carnivores (e.g. felids). As you go from animals that eat a large amount of difficult-to-digest matter (cellulose, in particular) to easy-to-digest matter (meat), they have fewer stomachs and shorter GI tracts, and food moves through their bodies more quickly.

If your aliens ate meat, it would probably go through quickly. If they have two stomachs and a long GI tract, they probably eat a lot of plant matter that takes longer to break down into useful nutrition.

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  • $\begingroup$ That makes sense. So two stomachs is more for longer digestion. $\endgroup$ – swilson225 Jun 17 '20 at 16:33
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    $\begingroup$ This also depends on what is meant by "more". Herbivores tend to eat large volumes of low calorie food, carnivores small volumes of high calorie food. So measured in volume the herbivore may eat more, but measured in calories the carnivore might. $\endgroup$ – jamesqf Jun 17 '20 at 18:56
  • $\begingroup$ You could have mentioned that ruminants have 4 stomachs (arranged more or less in series, not in parallel) in your answer... $\endgroup$ – Level River St Jun 17 '20 at 23:35
  • $\begingroup$ Maybe worth adding the meaning of GI in the answer ? $\endgroup$ – ThePainfull Jun 18 '20 at 12:11
  • $\begingroup$ @LevelRiverSt Yeah, I'm not sure what purpose having parallel stomachs would serve, unless there's some other organ before them that somehow distinguishes, say, meat from vegetables, sending plant matter to the slow stomach and meat to the fast one? I haven't heard of any such thing existing in nature. $\endgroup$ – Darrel Hoffman Jun 18 '20 at 13:30
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Not exactly

Stomachs are a mechanism for digestion. The amount of food a human consumes on a daily basis has very little to do with the size of the stomach, and has more to do with the amount of energy said humans expends. Or, more correctly, the causation arrows are flipped - the size of the stomach is based on how much food a human needs to eat, not the amount a human needs to eat being dependent on the size of the stomach. The concept of 'overeating' or eating more food than your body needs is a trait used to store surplus energy.

Why would a creature have multiple stomachs? Well, as you guesses, a larger digestive system. Complex and mostly indigestible foods (i.e. grass) require a long digestive system to handle. Koalas, for instance, having an incredibly long and complex digestive system and it's basically just for eucalyptus leaves. Having two stomachs help digestion, and that's why your aliens have them. As for the biology - well, you have choices. Multiple stomachs can be connected to another, as in Stomach A leads to Stomach B, or a mouth will lead to both of them and the creature will force food from one stomach back into the mouth before sending it to the second stomach. Or, in the case of ruminants, both!

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  • $\begingroup$ "the causation arrows are flipped"; yup, exactly what I said. (Looking at the timestamps, it's obvious that we were both typing similar answers at the same time 😉.) $\endgroup$ – Matthew Jun 17 '20 at 14:58
  • $\begingroup$ @Matthew Yup. I just got ninja'd is all. $\endgroup$ – Halfthawed Jun 17 '20 at 15:56
  • $\begingroup$ You don't need a bigger/multiple stomach(s) to eat more. However, overeating can cause bloating and/or weight gain. Multiple stomachs is mostly for helping with longer digesting and food that is hard to digest. I don't think my aliens will have a hard time digesting food. $\endgroup$ – swilson225 Jun 17 '20 at 16:37
  • $\begingroup$ @swilson225 If they won't have a problem digesting food, then they don't need multiple stomachs. $\endgroup$ – Halfthawed Jun 17 '20 at 17:15
  • $\begingroup$ Yeah, they won’t be needing multiple stomachs! $\endgroup$ – swilson225 Jun 17 '20 at 17:17
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Having had my complete large intestine surgically removed a couple of years ago, I have a bit of relevant first hand experience here :)

At least in humans, the function of the stomach is to break down food chemically, but the function of he GI tract is to process it further (using the diverse population of micro-organisms which live there because it is a less hostile environment than the stomach) and also to recycle fluids back into the body by absorbing them instead of excreting them.

Removing part of the GI tract decreases the "transit time" of food through the system, which means that some vegetables (e.g. peas and sweet corn) are not "digested" at all and emerge looking pretty much the same as when you ate them. There is also a significantly higher loss of both fluids and electrolytes - for example I now typically need at least 3 liters of fluid per day to stay properly hydrated, and high-salt foods are not "unhealthy junk" but a necessary part of my diet!

So having multiple stomachs on its own doesn't necessarily have much benefit, unless, like ruminants, you can recycle material between GI tract and one or more stomachs, to repeat the two processes of breaking it down chemically, and absorbing the nutrients from it.

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  • $\begingroup$ Hm, interesting! Thanks for sharing! $\endgroup$ – swilson225 Jun 17 '20 at 23:56
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It might digest faster, at least the part that regards the stomach, as there are 2 stomachs doing the job and thus there's a better chance of a larger contact surface, though I can't say with absolute certainty. Regarding how much food, a stomach is an organ that requires a decent amount of maintenance, so keeping 2 of them will likely require more resources and thus more food.

Though to be truly honest, it sounds better to just have one larger stomach, as I don't think the second stomach would speed up this part of the digestive process to make up for their maintenance and energy cost. Additionally, the stomach is but a single part of digestion, with the main nutrient absorption happening at the intestines, so I don't see enough advantages in more than one stomach to make its presence worth the extra energy, nutrients and space required. Cows for example, rather than growing another stomach, simply divided their single stomach in 4 main divisions to fit their diet, so here's an example of how a single stomach can already do what's needed for it.

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  • $\begingroup$ I was taking the larger stomach in consideration. Multiple stomachs may not be needed. $\endgroup$ – swilson225 Jun 17 '20 at 16:38
  • $\begingroup$ @swilson225 well our own stomachs will actually dilate and increase in size, should we if we eat too much, so simply having one larger stomach instead of 2 smaller ones seems like the best way to go and will likely be linked to a larger food intake, just like our stomachs expand to accommodate the increased food intake. $\endgroup$ – ProjectApex Jun 17 '20 at 16:46
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    $\begingroup$ Yep, that’s true and I agree. The larger the stomach, the more food you can take in without (presumably) getting fat (storing extra food you don’t need). My aliens won’t overeat like humans. They eat what they need. $\endgroup$ – swilson225 Jun 17 '20 at 17:16
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Two stomachs would be a great advantage. It isn't uncommon for a lot of animals on earth. Read about microbiotic digestion. A lot of bacterias can digest things, a human cannot digest. Rabbits eat their own excrement to gain advantage of the extra proteins produced by the bacterias, because they do not have a second stomach. With a second stomach, you could digest the bacteria like a cow. But digestion could be slow because bacterias need to grow in the first stomach.

So, an humanoid with two stomachs could survive with a really meager vegetation for food and would need less food than an ordinary human. But there could be some problems with gas, it might be inconvenient for us to live with such an humanoid in the same house.

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  • $\begingroup$ Oh my! The gas! How wonderful XD $\endgroup$ – swilson225 Jun 17 '20 at 19:39
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There is a big difference between whether the stomachs of your alien are aligned in parallel or in series:

In Series: Food which is entering the body, enters the different stomachs one by one. This has been answered already: a number of plant-eating animals have multiple stomachs, which are used to digest food which is difficult to digest.

In Parallel:

  • Two different stomachs might be used to digest different kinds of food. I don't think this is something that occurs on earth (correct me when wrong). But I can imagine that the fluids in the stomachs can be of a different nature. So the alien's body could choose which stomach to use to digest the food he takes in, allowing him to diverge the types of food he can digest.
  • Two stomachs of the same type (so without different 'fluids') could be treated the same as a bigger stomach. A bigger stomach for the same amount of food intake has the advantage that the alien doesn't have to eat that often. Our eating pattern is (amongst other factors) defined by our stomach size: if our stomach is full, we have to stop eating. If our stomach would be 10 times as big, we could survive by eating only once per week (hypothetically of course: there are more factors playing here besides the stomach size). Snakes for example are known for their big stomach-to-body ratio.
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  • $\begingroup$ Heads-up: the multiple stomachs bit is a myth. The plant eating animals you refer to have a single stomach divided in 4 sections. Watch out for the relation between stomach size and how often you feed, as snakes will need to feed often unless they get large prey. A bigger stomach means you can ingest more food, but not eating often means using this stomach to digest large amounts of food in short periods (what will allow a big snake to stay months without eating isn't only the stomach that can fit a deer, but the deer sized meal it puts inside it). $\endgroup$ – ProjectApex Jun 18 '20 at 11:13

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