# Allowing humans to digest cellulose
**URL:** https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966
**Category:** Factual Questions
**Created:** [August 22, 2008, 9:22pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966 "2008-08-22T21:22:10Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@ntcrawler](https://boards.straightdope.com/u/ntcrawler)
#### Post date: [August 22, 2008, 9:22pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/1 "2008-08-22T21:22:10Z")
Cellulose fiber. Found in a wide variety of plants. Digestible by animals, but not by humans, because we lack certain types of bacteria in our digestive tract to break it down. Would it be possible to somehow introduce the necessary little critters? It seems like it would be a good way to help fight worldwide hunger if we could somehow increase the variety of foods that we can consume. Instead of having to cultivate we could just rub elbow to elbow with Pandas and munch on some eucalyptus leaves. Is this possible? What would be the downside?
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### Author:  [@foolsguinea](https://boards.straightdope.com/u/foolsguinea)
#### Post date: [August 22, 2008, 9:50pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/2 "2008-08-22T21:50:12Z")
So, what, you going to surgically alter everyone’s GI tract to support the new monera?
Ruminants also chew their cud to facilitate this. I’m not sure what that would do to human teeth, but I guess that’s the most manageable part of the re-engineering.
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### Author:  [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)
#### Post date: [August 23, 2008, 3:01am UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/3 "2008-08-23T03:01:08Z")
[QUOTE=ntcrawler]
What would be the downside?
[/QUOTE]
There isn’t much energy in cellulose. Ruminants spend most of their time chewing cud. Actually, not all that different from office drones and microwave popcorn, I suppose. However, until you come up with a cultivar of grass that doesn’t taste like…grass, then I don’t think your plan is going to sell well.
Stranger
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### Author:  [@astro](https://boards.straightdope.com/u/astro)
#### Post date: [August 23, 2008, 3:27am UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/4 "2008-08-23T03:27:42Z")
[QUOTE=ntcrawler]
What would be the downside?
[/QUOTE]
Every trip to the bathroom will require you take a along an industrial strength plunger to force down your Kong sized feces.
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### Author:  [@Attack\_from\_the\_3rd\_dimension](https://boards.straightdope.com/u/Attack_from_the_3rd_dimension)
#### Post date: [August 23, 2008, 3:28am UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/5 "2008-08-23T03:28:28Z")
I’m thinking that the farts are going to be wicked.
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### Author:  [@Derleth](https://boards.straightdope.com/u/Derleth)
#### Post date: [August 23, 2008, 3:39am UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/6 "2008-08-23T03:39:29Z")
[QUOTE=Attack from the 3rd dimension]
I’m thinking that the farts are going to be wicked.
[/QUOTE]
The farts are going to be methane, which is quite wicked as a greenhouse gas but can (in theory) be used as fuel. Which means we might be required to capture our farts to help fuel our cars.
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### Author:  [@Cerowyn](https://boards.straightdope.com/u/Cerowyn)
#### Post date: [August 23, 2008, 7:32am UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/7 "2008-08-23T07:32:35Z")
[QUOTE=ntcrawler]
Instead of having to cultivate we could just rub elbow to elbow with Pandas and munch on some eucalyptus leaves.
[/QUOTE]
Unless you’re suggesting altering pandas, I suspect that you either mean “elbow to elbow with Koala Bears” or “munch on some bamboo shoots.”
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### Author:  [@Anaglyph](https://boards.straightdope.com/u/Anaglyph)
#### Post date: [August 23, 2008, 11:54am UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/8 "2008-08-23T11:54:02Z")
[QUOTE=Stranger On A Train]
There isn’t much energy in cellulose. Ruminants spend most of their time chewing cud. Actually, not all that different from office drones and microwave popcorn, I suppose. However, until you come up with a cultivar of grass that doesn’t taste like…grass, then I don’t think your plan is going to sell well.
Stranger
[/QUOTE]
Theoretically, there is as much energy in cellulose as in starch - both are built of glucose building blocks. However, the geometry of the bond between the building blocks is different, and we lack the enzyme to break down the cellulose variety of this bond in digestion. In addition, the cellulose fibers pack more densely, making them harder to attack for the appropriate enzymes.
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### Author:  [@Attack\_from\_the\_3rd\_dimension](https://boards.straightdope.com/u/Attack_from_the_3rd_dimension)
#### Post date: [August 23, 2008, 2:45pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/9 "2008-08-23T14:45:06Z")
[QUOTE=Derleth]
The farts are going to be methane, which is quite wicked as a greenhouse gas but can (in theory) be used as fuel. Which means we might be required to capture our farts to help fuel our cars.
[/QUOTE]
So this is now a multi-phase project - I suggest that you and I start working on the fart powered car, while the rest of the board members spend their time trying to digest bamboo.
(Dude, we totally scored the good assignment!)
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### Author:  [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)
#### Post date: [August 23, 2008, 3:06pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/10 "2008-08-23T15:06:04Z")
I’m way ahead of you guys. I ate grass a few times as an undergrad. Usually it was cooked into some nice baked goods like brownies or cookies.
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### Author:  [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)
#### Post date: [August 23, 2008, 3:26pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/11 "2008-08-23T15:26:27Z")
[QUOTE=Anaglyph]
Theoretically, there is as much energy in cellulose as in starch - both are built of glucose building blocks. However, the geometry of the bond between the building blocks is different, and we lack the enzyme to break down the cellulose variety of this bond in digestion. In addition, the cellulose fibers pack more densely, making them harder to attack for the appropriate enzymes.
[/QUOTE]
I’ve never understood why exactly cellulose is harder to break down than other starches. I know that most starches have alpha glycosidic bonds, while cellulose uses beta glycosidic bonds, but to me that seems like a fairly insignificant difference in geometry. There seem to be lots of very fast, efficient enzymes capable of breaking the alpha bonds. Why are the beta bonds more difficult to hydrolyze?
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### Author:  [@ratatoskK](https://boards.straightdope.com/u/ratatoskK)
#### Post date: [August 23, 2008, 3:43pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/12 "2008-08-23T15:43:11Z")
It might work if you eat termites at the same time as you swallow a few tree limbs.
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### Author:  [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)
#### Post date: [August 23, 2008, 8:04pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/13 "2008-08-23T20:04:53Z")
[QUOTE=ratatoskK]
It might work if you eat termites at the same time as you swallow a few tree limbs.
[/QUOTE]
Or beavers
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### Author:  [@ntcrawler](https://boards.straightdope.com/u/ntcrawler)
#### Post date: [August 23, 2008, 9:57pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/14 "2008-08-23T21:57:40Z")
So would it be possible to introduce those enzymes into our digestive tract?
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### Author:  [@BrotherCadfael](https://boards.straightdope.com/u/BrotherCadfael)
#### Post date: [August 23, 2008, 11:27pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/15 "2008-08-23T23:27:31Z")
As far as I can tell, humans have every right to digest cellulose. Not sure why the OP thinks it is “not allowed”.
Of course, humans lack the ability to do so, but that is a whole different question.
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### Author:  [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)
#### Post date: [August 24, 2008, 1:20am UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/16 "2008-08-24T01:20:09Z")
[QUOTE=ntcrawler]
So would it be possible to introduce those enzymes into our digestive tract?
[/QUOTE]
The reason humans can’t digest cellulose is that our entire digestive tract is not properly designed for it. Changing any one thing won’t help.
Herbivores have to be designed from their teeth on down to accommodate plant material. They need lots of flat grinding teeth to crush the fiber and wear it down to a manageable size. They need extra stomachs to hold cud that can be brought up to be chewed at length, like cows. Or they need to eat their own poop to extract nutrients that didn’t get absorbed the first time through, like [rabbits](http://en.wikipedia.org/wiki/Rabbit#Cecal_pellets).
> [@](#):
>
> Rabbits are hindgut digesters. This means that most of their digestion takes place in their large intestine and cecum. In rabbits, the cecum is approximately 10 times bigger than the stomach, and it, along with the large intestine, makes up roughly 40% of the rabbit’s digestive tract.[2] Cecotropes, sometimes called “night feces”, come from the cecum and are high in minerals, vitamins and proteins that are necessary to the rabbit’s health. Rabbits eat these in order to meet their nutritional requirements. This process allows rabbits to extract the necessary nutrients from their food.
And the bacteria can’t live just anywhere in the intestines, which BTW are much longer than human intestines. They inhabit the cecum, which humans lack in working form.
So much would have to be altered to allow humans to eat and digest cellulose than the result wouldn’t be human any more. It’s certainly not anything remotely within the scope of today’s technology or biology.
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### Author:  [@ntcrawler](https://boards.straightdope.com/u/ntcrawler)
#### Post date: [August 24, 2008, 5:04am UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/17 "2008-08-24T05:04:45Z")
[QUOTE=Exapno Mapcase]
The reason humans can’t digest cellulose is that our entire digestive tract is not properly designed for it. Changing any one thing won’t help.
So much would have to be altered to allow humans to eat and digest cellulose than the result wouldn’t be human any more. It’s certainly not anything remotely within the scope of today’s technology or biology.
[/QUOTE]
Interesting… How does this compare to Pandas and Koalas? IIRC they don’t eat their poop and don’t chew their cud. What’s their method for digesting the cellulose?
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### Author:  [@Sunspace](https://boards.straightdope.com/u/Sunspace)
#### Post date: [August 24, 2008, 5:34am UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/18 "2008-08-24T05:34:43Z")
[QUOTE=Saint Cad]
Or beavers
[/QUOTE]
I ate a beaver once…
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### Author:  [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)
#### Post date: [August 24, 2008, 3:25pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/19 "2008-08-24T15:25:46Z")
[QUOTE=ntcrawler]
Interesting… How does this compare to Pandas and Koalas? IIRC they don’t eat their poop and don’t chew their cud. What’s their method for digesting the cellulose?
[/QUOTE]
Sloth.
> **[Giant panda](https://en.wikipedia.org/wiki/Giant_Panda)**
>
> The giant panda (Ailuropoda melanoleuca), also known as the panda bear or simply panda, is a bear species endemic to China. It is characterised by its white coat with black patches around the eyes, ears, legs and shoulders. Its body is rotund; adult individuals weigh 100 to 115 kg (220 to 254 lb) and are typically 1.2 to 1.9 m (3 ft 11 in to 6 ft 3 in) long. It is sexually dimorphic, with males being typically 10–20% larger than females. A thumb is visible on its forepaw, which helps in hold...
> [@](#):
>
> Despite its taxonomic classification as a carnivore, the panda has a diet that is primarily herbivorous, which consists almost exclusively of bamboo. However, pandas still have the digestive system of a carnivore and do not have the ability to digest cellulose efficiently, and thus derive little energy and little protein from consumption of bamboo. The average Giant Panda eats as much as 9 to 14 kg (20 to 30 pounds) of bamboo shoots a day. Because pandas consume a diet low in nutrition, it is important that they keep their digestive tract full. The limited energy input imposed on them by their diet has affected the panda’s behavior. Pandas tend to limit their social interactions and avoid steeply sloping terrain in order to limit their energy expenditures.[15]
>
> Two of the panda’s most distinctive features, its large size and its round face, are adaptations to its bamboo diet. Panda researcher Russell Ciochon observed that: “[m]uch like the vegetarian gorilla, the low body surface area to body volume [of the giant panda] is indicative of a lower metabolic rate. This lower metabolic rate and a more sedentary lifestyle allow the giant panda to subsist on nutrient poor resources such as bamboo.”[15] Similarly, the panda’s round face is the result of powerful jaw muscles, which attach from the top of the head to the jaw.[15] Large molars crush and grind fibrous plant material.
Note the totally different jaw and tooth system as well. In other words, to convert a human to eating cellulose you’d have to turn them into something like pandas.
If you want to counterargue that you were thinking of a hybrid with a part cellulose part higher energy diet, you still have to figure out a way to balance systems optimized for two poles; low-energy, low-metabolism and high-energy, high-metabolism. I don’t see how you could start with one chassis and achieve both.
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### Author:  [@DesertDog](https://boards.straightdope.com/u/DesertDog)
#### Post date: [August 24, 2008, 3:54pm UTC](https://boards.straightdope.com/t/allowing-humans-to-digest-cellulose/460966/20 "2008-08-24T15:54:02Z")
[QUOTE=Attack from the 3rd dimension]
I’m thinking that the farts are going to be wicked.
[/QUOTE]
Carnivore farts are a lot worse than herbavores; ask any cat owner.
Do multi-chamber ruminents (like cows) actually digest cellulose ala termites and their gut bacteria? I had the impression cud-chewing was to give the plant material a good working over so as to extract every last smidge of nutrition.
Non cud-chewing herbivores definitely don’t. Horse droppings look pretty much like hay, only wetter and birds like to work them over for unutilized grain.
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