I have a genius new idea, that could not possibly fail. What if... we would use the methane created during digestion and use it to create even more energy and biomass. The idea of this process was borrowed from underwater bacteria that are too deep for the sunlight to reach them.

What effects would the ability to use methane, in similar to these microbes, on mammals be?

More precisely, would the extra energy gained in this route be significant?

  • $\begingroup$ Not a lot, digestion is already incredibly efficient and methanotrophy requires oxygen which means you have to get the methane into the bloodstream, which will require energy, and will not produce much ATP. $\endgroup$ – John Apr 15 '17 at 18:33
  • $\begingroup$ @John uhmm... $\endgroup$ – Mephistopheles Apr 15 '17 at 18:43
  • $\begingroup$ Making a full answer $\endgroup$ – John Apr 15 '17 at 19:05

In humans I think a trivial amount of carbon intake is converted to methane. Ruminant livestock supposedly produce a lot more. I am not sure why methanotrophs in the rumen do not gobble it all up.

The idea of reducing methane production is interesting because of the below linked in which methane production is tied to weight gain. Either 1:methane has pharmacologic effects itself; not impossible given the small size of the molecule and fat solubility. 2: the presence of methanogens somehow augments metabolism and caloric benefit from food. 3: an absence of methanotrophs augments metabolism.

From https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3277195/

Methanogens have been shown to affect caloric harvest by increasing the capacity of polysaccharide-eating bacteria to digest polyfructose-containing glycans, which leads to increased weight gain in mice.14 Further, previous studies by our group have demonstrated that methane gas slows proximal small intestinal transit by 59% in an in vivo model.15 This slowing of proximal small intestinal transit may contribute to increased weight gain by increasing the total gut microbiome load or the amount of time during which energy is harvested from meals. Given the associations between methanogens and weight gain in animal models, coupled with the finding of an association between methane and delayed transit, this study hypothesized that human subjects with increased concentrations of methane on breath testing might exhibit increased levels of obesity compared to individuals without elevated methane concentrations.

One would conclude from this that if you wanted to optimize caloric benefit from food you should increase or facilitate methane production. That is not ideal for first worlders humans who suffer from obesity but would be hugely useful for pig farming, where an additional 5% of weight gain for the same feed mass is pure profit.

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Not a lot, digestion is already incredibly efficient and methanotrophy requires oxygen which means you have to get the methane into the bloodstream, which will require energy, and will not produce much ATP.

the real kicker is energy density and how much we produce. A human produces at max about 10 milligrams of methane a day. Methane has an energy density of 53.6 MJ/Kg, so all the methane a person produces in a day yields about 0.0128 food calories. For comparison there is about ~10 food calories in a single potato chip and about 3.5 food calories in a single oyster cracker.

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  • $\begingroup$ I wouldn't think digestion is all that efficient. After all, if the end product from most mammals is dried, it will burn quite well: en.wikipedia.org/wiki/Dry_animal_dung_fuel $\endgroup$ – jamesqf Apr 15 '17 at 19:38
  • $\begingroup$ well that's true of almost anything organic, and keep in mind that is herbivore feces, much of that is fiber, human feces for instance is almost entirely dead bacteria. Plus efficiency is relative compared to say a steam engine or almost any other non-organic energy extraction digestion is incredibly efficient. $\endgroup$ – John Apr 15 '17 at 22:56
  • $\begingroup$ I still have problems seeing the efficiency of digestion, considered purely as energy extraction. Lots of residual energy in feces, at least mammalian ones. Of course energy extraction is not its only goal: it must also extract various building blocks like amino acids. $\endgroup$ – jamesqf Apr 17 '17 at 4:40
  • $\begingroup$ try comparing it to any other energy extraction means and you will see it, don't let the residue confuse you, for most fuel based artificial energy extraction methods most of the energy released is never used, a gasoline engine only uses about 25% of the energy and even a steam power plants only manages 40%. Biological systems hit their limit not at digestion (refining) but at ATP production which is only about 40% efficient. $\endgroup$ – John Apr 17 '17 at 15:02
  • $\begingroup$ for a normal human we uptake about 95% of all the nutrients in our food with the exception of fiber (0-1%). Of course things like overeating can drop that. Herbivores have huge digestive systems becasue extracting energy from cellulose(fiber)is difficult (think of it as burning plastic instead of oil) so many organisms just ignore it. Herbivores are stuck with it becasue the bulk of their diet is fiber. $\endgroup$ – John Apr 17 '17 at 15:24

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