|MadSci Network: Anatomy|
Cellulose is processed to a limited extent in the human gut by bacteria. The main limitation to this processing is probably retention time. The purpose of the caeca of herbivorous mammals is to hold the food for a longer period than would be possible in a simple tubular gut. The human caeca, known as the appendix, is very small, and I don't know whether it is possible for food to enter it. If food did enter the human caeca, then it would be acted on by bacteria just as would happen in the gut. The passage of food through the caeca of a herbivorous mammal and the maintenance of the ecosystem of micro-organisms which break down large quantities of cellulose are complex processes which would require a long period of evolution to re-create in humans. I doubt that they could be created by short-term genetic manipulation.
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