I've read that cellulose has a lot of calories that go unused. I was wondering how practical it would be to incorporate a bacteria capable of suggesting cellulose into the human gut.

I would say that it is worth it if a human could gain a substantial amount of calories by digesting cellulose in a "normal" diet. To compute the amount of calories, I would like estimates for how fast bacteria can process the cellulose (like half life per billion bacteria) and how efficient the process would be.

Then given the average duration of the digestive process and a reasonable bacteria population, estimates could be made on how much energy could be gained by digesting the cellulose in an average diet.


closed as primarily opinion-based by Remi.b, anongoodnurse, David, Bryan Krause, kmm Oct 10 '17 at 22:10

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  • $\begingroup$ It looks like you are confounding the verb suggest with the verb digest! Also, instead of practically, you probably meant practicality $\endgroup$ – Remi.b Oct 7 '17 at 21:41
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    $\begingroup$ Possible duplicate of Human Digestion of Cellulose? $\endgroup$ – Remi.b Oct 7 '17 at 21:43
  • $\begingroup$ @Remi.b Auto-correct likes to type for me! I'd say this isn't a duplicate because I am more interested in the economics of it. In the sense of "Can we get enough energy from the cellulose to make it worth it?". I'll edit the questions to make that clear. $\endgroup$ – aidan.plenert.macdonald Oct 7 '17 at 22:40
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    $\begingroup$ If you plan to alter the human microbiome, you should investigate the effect in an animal model, first. The human gut microbiome is largely important on an organismal basis. $\endgroup$ – CKM Oct 8 '17 at 7:07
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    $\begingroup$ Cellulose constitutes a major part of our dietary roughage. If you plan to modify the microbiome in the gut to break down the cellulose for us, it would result in the decrease of the bulk fiber, which increases the stool volume and finally result into constipation and painful mornings. I am not saying that cellulose is the only bulk fiber, but it does constitute a major part of it. $\endgroup$ – jyoti proy Oct 8 '17 at 7:32

You really need to understand how cellulase would effect metabolic systemic homeostasis before anyone can answer that. It's an interesting question. At first glance, one could consider that cellulase would allow disproportionate glucose intake, ultimately making fat a smaller % part of the diet. If unchecked, this could lead to a reverse Randal effect inhibiting fatty acid metabolism thus altering adipokine synthesis leading to a range of negative, if not, species detrimental effects such as reduced capacity for reproduction (as an example between altered biosynthesis and crosstalk between leptin and estrogen). This may have presented a problem for early humans, because in essence, cellulose could have acted as the very first mcdonalds convienience if we were capable of digesting it. I'm sure I'm missing many complications that would have occurred if early humans had this capacity, but it's a nice thought experiment.

And regarding the mathematical induction, forget about it, you can't induce a conclusion on potential alterations within the mammalian digestive system from only the enzyme kinetics of cellulase found in bacteria.

  • $\begingroup$ When you say you can't do the math induction, why can't you just put upper bounds on the energy intake? I've done this for things like having chlorophyll in our skin. With chlorophyll, it was something like you'd need to spend >24hrs in bright sunlight to get 200kcal around 95% confidence. Clearly not worth it. I thought cows have a bacteria that digests bacteria. Can't you make estimates using that as a model? $\endgroup$ – aidan.plenert.macdonald Oct 8 '17 at 2:46
  • $\begingroup$ It's quite complicated to explain actually. Your best bet would be to somehow model the ruminant 24-hour diet AND digestive system required to extract enough energy from low-efficiency fibers (cellulose containing) as an equivalent human model. But dang, you're gonna have a lot of caveats and complications to make a useable conclusion, not to mention cows can digest meats as humans do, making their similarity more of an systems biology obstacle. Also, you have to consider the location and distribution of all the enzymes within the digestive tract; and the differences in analogue $\endgroup$ – Aaron43 Oct 8 '17 at 3:16
  • $\begingroup$ efficiency - I know it doesn't sound so important at first but enzyme location in the gut can dramatically effect metabolite uptake and usability. My best guess would be to identify if anyone has measured blood glucose levels of a human who mimicked a cow for 24-72 hours; & from there you could somehow create a type of weighting to better interpret cow digestion to human applicability, at a high level. $\endgroup$ – Aaron43 Oct 8 '17 at 3:18
  • $\begingroup$ Or just create your own hypothetical human scenario, with enzyme density and tract location, but this could easily be done simply by giving someone an equivalent X amount of glucose that mimics the amount of to be digested cellulose (kinetics shouldn't be a major burden here). But still, the many biological optimization per species will create caveats in the conclusion; tho id still read about it lol $\endgroup$ – Aaron43 Oct 8 '17 at 3:20

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