View Full Version : Can Humans DIGEST Cellulose.. ??


srimukh
05-18-09, 12:17 AM
All herbivorus animals have enzyme called 'Cellulase', which digests the cellulose present in plants they eat.

But we lack that enzyme, but even then we can digest the RAW FRUITS & VEGETABLES we eat. How is that possible?
Does the remaining nutrients get digested and the left over cellulose is thrown out intact? :confused:

TFL
05-18-09, 12:21 AM
Does the remaining nutrients get digested and the left over cellulose is thrown out intact?
More or less, to my understanding. It's also known as fiber (http://en.wikipedia.org/wiki/Dietary_fiber) in this regard. ;)

scifes
05-18-09, 09:49 AM
as far as my knowledge goes cellulose isn't present in fruits..it's as TFL said a harder fiber used to support and enforce plants ..

but i think people USED to digest it..(cavemen)..that's one of the explenations for us having a cecum..

Enmos
05-18-09, 09:57 AM
as far as my knowledge goes cellulose isn't present in fruits..it's as TFL said a harder fiber used to support and enforce plants ..
Cellulose is present in fruit. It's the primary component of cell walls in green plants.

scifes
05-18-09, 10:05 AM
strangly enough..you're right..but i'm sure humans can't digest it..i guess it's just used as fiber instead of totally breaking it down..

Enmos
05-18-09, 10:11 AM
strangly enough..you're right..
Remarks like this is what makes you annoying.


but i'm sure humans can't digest it..i guess it's just used as fiber instead of totally breaking it down..
Humans cannot digest cellulose (or very poorly) because they don't produce cellulases.
Edit: To be more precise, humans lack the symbiotic bacteria that produce cellulases to help break down cellulose.

CharonZ
05-18-09, 01:12 PM
Precisely. No mammals produce cellulases, however certain other animals (as e.g. certain insects and mollusks) possess one. However, certain gut bacteria also found in humans are actually able to degrade cellulose but generally the amount appears to be too low to be significant.

ElectricFetus
05-18-09, 01:28 PM
Not only would we need cellulase but we would need multiple stomachs for the preprocessing of cellulose just so that the cellulases can do their works with high enough throughput to power our bodies, and even then we may need to live like sloths to reduce energy consumption.

scifes
05-19-09, 02:16 AM
Remarks like this is what makes you annoying.
lol, i didn't mean to offend you..only i was sure it was otherwise and research to find it's true, that's all



Humans cannot digest cellulose (or very poorly) because they don't produce cellulases.
Edit: To be more precise, humans lack the symbiotic bacteria that produce cellulases to help break down cellulose.
then what about #4?? is it really left and used as fiber?

scifes
05-19-09, 02:21 AM
Not only would we need cellulase but we would need multiple stomachs for the preprocessing of cellulose just so that the cellulases can do their works with high enough throughput to power our bodies, and even then we may need to live like sloths to reduce energy consumption.

you totally reminded me of cows..with their 5 stomachs...and digesting mechanism..

and cows are mammals(?) does that mean they digest it?

Enmos
05-19-09, 04:53 AM
lol, i didn't mean to offend you..only i was sure it was otherwise and research to find it's true, that's all
Ok fair enough.


then what about #4?? is it really left and used as fiber?
Yep. It aids the smooth working of our intestines. It prevents constipation for example.
To evolve the ability to digest cellulose now would probably not be very beneficial ;)

Pete
05-19-09, 07:57 PM
you totally reminded me of cows..with their 5 stomachs...and digesting mechanism..

and cows are mammals(?) does that mean they digest it?

Yes, although indirectly. The way I understand it is that in cows and other animals like them (including hippos, camels, sheep, deer, giraffe, and maybe even whales) cellulose is digested by bacteria in one of the stomachs, then the bacteria themselves are digested a little further on. Horses, elephants, rhinos, and pigs also digest cellulose through bacteria, but in a different way and not as efficiently.

I think termites digest wood (which is mostly cellulose) also via gut bacteria.

ElectricFetus
05-19-09, 08:30 PM
you totally reminded me of cows..with their 5 stomachs...and digesting mechanism..

and cows are mammals(?) does that mean they digest it?

they use bacteria to do it, and yes there body is pretty much dedicated to mulching cellulose so the bacteria can do their job, and they eat copious amounts to break even.

srimukh
05-20-09, 12:27 AM
no problem scifes. i think im satisfied with the point that cellulose is used as fiber.. for many puposes..:cool:

srimukh
05-20-09, 12:28 AM
no problem scifes. i think im satisfied with the point that cellulose is used as fiber.. for many puposes..:cool:

scifes
05-20-09, 01:54 AM
no problem scifes. i think im satisfied with the point that cellulose is used as fiber.. for many puposes..:cool:

yippee!
so i'm not the only one having posting problems..:)

Giambattista
05-20-09, 05:35 AM
What I am wondering is how much of an impedance is cellulose to assimilation of nutrients. I know it probably depends on the food.

Giambattista
05-20-09, 05:42 AM
Vegetables, cellulose, and nutrient absorption!

http://fernsfronds.blogspot.com/2009/04/nutrition-note-cooking-carrots.html



Another study in 2002 showed that cooking carrots increases their level of beta-carotene. Beta-carotene belongs to a group of antioxidant substances called carotenoids, which give fruits and vegetables their red, yellow, and orange colorings. The body converts beta-carotene into vitamin A, which plays an important role in vision, reproduction, bone growth and regulating the immune system.

The downside of cooking vegetables is that it can destroy some of the vitamin C in them. The reason is that Vitamin C, which is highly unstable, is easily degraded through oxidation, exposure to heat (it can increase the rate at which vitamin C reacts with oxygen in the air) and through cooking in water (it dissolves in water).

So in reality, unlike most other vegetables (though not all), carrots are more nutritious when eaten cooked than eaten raw (except when juiced). Because raw carrots have tough cellular walls, the body is able to convert less than 25 per cent of their beta carotene into vitamin A. Cooking, however, partially dissolves cellulose-thickened cell walls, freeing up nutrients by breaking down the cell membranes.

From http://www.carrotmuseum.co.uk/nutrition.html

Fraggle Rocker
05-20-09, 10:20 PM
The way I understand it is that in cows and other animals like them (including hippos, camels, sheep, deer, giraffe, and maybe even whales) cellulose is digested by bacteria in one of the stomachs. . . .Cetaceans are indeed artiodactyls. Based upon DNA analysis they were recently discovered to be descended from primitive hippopotamuses. Cetacea was demoted from an order to a suborder of Artiodactyla. However, all whales and dolphins are carnivores. The artiodactyl digestive system, supremely adapted for the digestion of cellulose, has evolved completely into a carnivorous digestive system. The baleen whales filter krill (tiny crustaceans) while the toothed whales (sperm whales and dolphins) are predators who hunt fish, or, in the case of the orca, other mammals and perhaps aquatic birds.

This is an example of how easily two closely related animals can have entirely different diets: the hippopotamus grazes, the porpoise fishes. I brought this up on the thread about eating meat: gorillas are herbivores who can get their calories from cellulose; humans aren't and can't.

Pete
05-20-09, 11:47 PM
Cetaceans are indeed artiodactyls. Based upon DNA analysis they were recently discovered to be descended from primitive hippopotamuses. Cetacea was demoted from an order to a suborder of Artiodactyla. However, all whales and dolphins are carnivores. The artiodactyl digestive system, supremely adapted for the digestion of cellulose, has evolved completely into a carnivorous digestive system.
Interestingly and unlike other carnivores, cetaceans do have a forestomach with a fermentation role in digestion like ruminants.

charles brough
05-21-09, 05:50 AM
i think people USED to digest it..(cavemen)..that's one of the explenations for us having a cecum..

fascinating . . . ! I am not disputing that, but it seems unlikely to me. Do you have any other information on this? What has the cecum to do with digesting cellulose? Are you saying that "cavemen" were "people" (homo sapiens)? How could we have evolved out of cellulose digestion in a hundred thousand years or so instead of millions of years? . . .just curious.:)

charles
http://atheistic-science.com

Enmos
05-21-09, 05:56 AM
fascinating . . . ! I am not disputing that, but it seems unlikely to me. Do you have any other information on this? What has the cecum to do with digesting cellulose? Are you saying that "cavemen" were "people" (homo sapiens)? How could we have evolved out of cellulose digestion in a hundred thousand years or so instead of millions of years? . . .just curious.:)

charles
http://atheistic-science.com

It seems very likely to me. But I don't know about people (cavemen).. lol
Humans evolved from leaf-eating primates, which in turn evolved from other plant-eating mammals.
It's not just likely, it must be true that human's ancestors were able to digest cellulose.

srimukh
05-29-09, 06:35 AM
but we are very much refined by millions of years of evolution from ancient primates... so, evolution should bring some beneficial characteristics and add more and more abilities to that organism.... even we are omnivorous... why we would lose that ability to digest cellulose.? in the previous replies, we read that cellulases are secreted by some bacteria present in the guts of herbivorous animals.. so did our ancestors eat some kind of food that would lead to formation of these bacteria???? did these bacteria come from the food they ate?? :confused:

CharonZ
05-29-09, 12:02 PM
Evolution is not about adding abilities. If there is no selective pressure to maintain them, abilities are as easily lost.
Generally, cellulose is digested with the help of bacteria and protozoa as mentioned above. While some may eventually come in with the food, much is of the flora is also inoculated by the mother.

ElectricFetus
05-29-09, 12:32 PM
Evolution is not about adding abilities. If there is no selective pressure to maintain them, abilities are as easily lost.
Generally, cellulose is digested with the help of bacteria and protozoa as mentioned above. While some may eventually come in with the food, much is of the flora is also inoculated by the mother.

Very true take a look a predators, they actually have lost vitamin production capabilities because they don't need them anymore since they started eating meat.

Fraggle Rocker
05-29-09, 02:30 PM
Are you saying that "cavemen" were "people" (Homo sapiens)? How could we have evolved out of cellulose digestion in a hundred thousand years or so instead of millions of years? When people say "cavemen" they loosely refer to all the ancestral genera and species of Homo sapiens after the family split off from the chimpanzee family, several million years ago. This includes, for example, Australopithecus.

Presumably the very first hominids must have been grazers like their ancestors. The adaptation to become the apex predator of the entire global ecosystem happened slowly.

srimukh
06-23-09, 08:55 AM
yes, so we cannot derive energy out of cellulose.right?

Fraggle Rocker
06-23-09, 11:39 AM
yes, so we cannot derive energy out of cellulose.right?Not without cooking it and breaking down the cellular structure. This is why fire was a key technology. There would have been no point in inventing the subsequent technology of farming if we couldn't cook the grains.

srimukh
07-15-09, 05:07 AM
cool.

DRZion
07-16-09, 12:08 PM
I thought it would be cool to develop a pill that would contain cellulose degrading bacteria. You would dump a bunch of grass, leaves, whatever in a pot, throw in a pill, and after some (lots) stirring, it could be edible. Does anyone see why this couldn't be done?

This could be a very handy tool for wilderness expeditions (as an emergency backup) or as a safeguard against natural disasters. At the same time, it would give people another incentive to tear down forests, so it would have to be controlled too.

srimukh
07-17-09, 09:45 AM
I thought it would be cool to develop a pill that would contain cellulose degrading bacteria. You would dump a bunch of grass, leaves, whatever in a pot, throw in a pill, and after some (lots) stirring, it could be edible. Does anyone see why this couldn't be done?

This could be a very handy tool for wilderness expeditions (as an emergency backup) or as a safeguard against natural disasters. At the same time, it would give people another incentive to tear down forests, so it would have to be controlled too.

good idea DrZion..:)
but, do u think That bacteria will survive the harsh washout by HCL acid?
I think HCL helps in destroying the bacteria and other microbes that enterering our digestive system......:confused:

Barbie
07-17-09, 01:46 PM
Not really, we can't extract calories from cellulose because we lack the acids and bacterial culture necessary, our stomach acid is really quite pathetic. We also don't have long enough intestines, so eating plants full of cellulose won't help us in desperate times. Eating raw plants will probably make you shit out forest green cinder blocks, your farts would be really loud and smell like spraypaint, and your colon would be irritated and swollen - so incredibly swollen.

Fraggle Rocker
07-17-09, 06:40 PM
What I am wondering is how much of an impedance is cellulose to assimilation of nutrients.It's a stonewall impediment. We can't digest enough of the nutrients embedded in uncooked cellulose to pay us back for the energy of chewing. As I mentioned earlier on this thread, fire is on the short list of nominees for the Breakthrough Technology that allowed H. sapiens to become us. One of the many things that cooking does is simply make food easier to eat. I recently saw a calculation that even if we didn't have to hunt our meat, it would take about four hours a day to eat a day's ration of it raw. That alone gives us a lot of time for other pursuits that advance civilization.
but we are very much refined by millions of years of evolution from ancient primates... so, evolution should bring some beneficial characteristics and add more and more abilities to that organism.... even we are omnivorous... why we would lose that ability to digest cellulose?Because we didn't need it any more. Grazing is an incredibly time-consuming activity. If you think spending four hours a day eating raw meat would be a bummer, try spending most of your waking life munching on raw plants. As we developed into hunters and adapted to a more carnivorous diet, we just didn't need to bother wasting our time chewing on roots, leaves and bark. A digestive system more compatible with a carnivorous diet would have been a favorable adaptation and evolution would have selected for it when it occurred. Herbivores have huge guts that would not make them nimble hunters.
in the previous replies, we read that cellulases are secreted by some bacteria present in the guts of herbivorous animals.. so did our ancestors eat some kind of food that would lead to formation of these bacteria???? did these bacteria come from the food they ate?? :confused:It's a stable bacterial culture that regenerates itself. Once it becomes established in the gut of a young animal a steady state exists in which the existing bacteria eat the cellulose and transform it into new bacteria, while at the same time the animal is digesting the protein-rich bacteria cells and keeping the population constant. I'm not sure how each species of herbivore establishes the initial culture, but baby rabbits, for example, eat the feces of adults in which there is inevitably some bacteria still alive.

The digestive help of bacteria is not limited to herbivores. Dogs and other canids have such short guts that they maintain a bacterial culture to help digest their food. In the wild they eat the intestines of their prey (and the leftovers from the meals of more finicky carnivores) to keep that culture going. If you see your dog out in the yard eating the feces of other animals, it's probably because you feed him commercial food full of preservatives and it's killing off his intestinal culture. He might even eat his own poop if he's desperate, some bacteria will have survived the onslaught of preservatives.
I thought it would be cool to develop a pill that would contain cellulose degrading bacteria. You would dump a bunch of grass, leaves, whatever in a pot, throw in a pill, and after some (lots) stirring, it could be edible. Does anyone see why this couldn't be done?Because it's so much easier to simply apply a nice flame to that pot and accomplish the same result by cooking. ;) High heat breaks down cellulose into simpler molecules like starches that we can digest. That's where this whole discussion started!

srimukh
07-19-09, 08:04 AM
Fraggle... that was a huge explanation. thank u:)

tommi123
08-16-09, 01:46 PM
No, we cannot digest cellulose. However, the microbes inside us can help us do it: they digest cellulose and we digest them.

Fraggle Rocker
08-17-09, 08:50 PM
No, we cannot digest cellulose. However, the microbes inside us can help us do it: they digest cellulose and we digest them.Only herbivores can do that. They have extremely long intestines that host an extensive bacterial culture. Food takes quite a while to pass through them so it gives the bacteria plenty of time to work. Some of them, the ruminants, have stomachs with multiple chambers in which different specific digestive processes take place. Cattle even regurgitate their food and run it through the cycle a second time.

Humans can't do any of those things. We do indeed host bacteria in our guts that help us digest our normal diet of protein, starch and sugar, but not cellulose. Even if we had cellulose-digesting bacteria, they could not stay in our relatively short digestive tract (compared to a sheep or a hippopotamus) long enough to do their job.

Billy T
08-20-09, 06:30 PM
... simply apply a nice flame to that pot and accomplish the same result by cooking. High heat breaks down cellulose into simpler molecules like starches that we can digest. ...I doubt that 100C (pot of boiling water at 1 atmosphere) can break down cellulose. A lot of money is trying to do that for second generation alcohol. AFAIK much higher temperatures and / or enzimes are required to break down cellulose. If I am wrong - please tell me.

DRZion
08-22-09, 08:36 PM
good idea DrZion..:)
but, do u think That bacteria will survive the harsh washout by HCL acid?
I think HCL helps in destroying the bacteria and other microbes that enterering our digestive system......:confused:

Crap, I keep getting lost all over these forums. Sorry for the delayed response.

Your point is valid. However, there are probably ways to engineer bacteria that could live even in our stomachs (since there are already some living species there). A problem may be toxic metabolites and the rate at which the breakdown of cellulose happens. This is why I think the bacteria should be free-living and added to batches of chopped up trees.

ZaccPF
08-30-09, 08:58 PM
Great discussions going on here

Fraggle Rocker
07-25-10, 12:37 AM
I doubt that 100C (pot of boiling water at 1 atmosphere) can break down cellulose. A lot of money is trying to do that for second generation alcohol. AFAIK much higher temperatures and / or enzymes are required to break down cellulose. If I am wrong - please tell me.Sorry, I missed your post last year. Yes, you're right. Heat does not break cellulose molecules down into simpler compounds that we can digest. It merely softens cellulose so that our digestive juices (aided by water) can squeeze between the molecules and digest the protein, starch and sugar that is unavailable to us in its natural state.

Almost no mammal has the enzymes to actually digest cellulose and use it as a source of calories. They require a bacterial culture to do that. (And when they say "almost no mammal," nobody every says who the exceptions are!)

Billy T
07-25-10, 08:07 AM
The only way for mammals to get energy from cellulose is to eat termites, etc. which do have the enzymes and/ or bacteria required. I think some monkeys or ape do this and thus get more out of the leaves etc. they eat.