And, perhaps why some are fat and some are skinny?
A good question to which there is only a limited answer yet.
Archaea do consume hydrogen gas generated in the gut, that inhibits bacterial growth; so bacteria function better and our food is more nutritious. The end product is methane.
“Methanobrevibacter smithii is the dominant archaeon in the human gut. It is important for the efficient digestion of polysaccharides (complex sugars) because it consumes end products of bacterial fermentation. Methanobrevibacter smithii is a single-celled micro-organism from the Archaea domain. M. smithii recycles hydrogen in methane, allowing for an increase in the transformation of nutrients into calories.”
“Researchers have sequenced M. smithii genome, indicating that M. smithii may be a therapeutic target for reducing energy harvest in obese humans.”
“The human gut microbiota has three main groups of hydrogen consuming microbes: methanogens including M. smithii, a polyphyletic group of acetogens, and sulfate-reducing bacteria.”
Importantly, of the 300-1000 different kinds of bacteria in the gut, though almost all the space is occupied by 30-40 different kinds, there are some bacteria that directly contribute to weight gain.
One such are those from the enterobacter genus.
“A recent study has shown that the presence of Enterobacter cloacae B29 in the gut of a morbidly obese individual may have contributed to the patient’s obesity. Reduction of the bacterial load within the patient’s gut, from 35% E. cloacae B29 to non-detectable levels, was associated with a parallel reduction in endotoxin load in the patient and a concomitant, significant reduction in weight.”