From what I understand (non-expert), meat does not have any fiber. I know that some parts of plants are not digestible by humans such as soluble and insoluble fiber. Even though we can not use these molecules directly, they are eaten by gut bacteria and thus are important for a healthy gut microbiome. Having a vibrant gut microbiome has a variety of positive health effects from regular poops to less inflammation.

I am curious if the gut bacteria obtain nutrients from other molecules in food especially from meat. I know that meat doesn’t have fiber, but does it have other types of molecules that can not be digested by humans but that can be broken down and used by gut bacteria?

Part of the reason why I think this may be possible is that human breast milk contains oligosaccharides, which are not digestible but that are important for the gut health of new born babies. Does meat contain any molecules such as these that are not digestible by humans? What are these molecules?

I think there must be some molecules in meat that are not digestible because animals on a purely carnivore diets still have gut bacteria (see this paper for example). These bacteria have to eat something.

I also posted a version of this question on Biology Stack Exchange.