Acetate, butyrate, and propionate are all very helpful to cellular processes. Soluble fiber specifically helps bacteria that make these for us.
Yet many of us live on near fiberless diets. Fiber is not needed to have gut bacteria. Gut bacteria vary with what is present. When fiber is present in the diet, the primary function of the extra bacteria is to provide things THEY need from the fiber.
https://www.thecarnivoredietcoach.com/news/carnivore-diet-gut-microbiome
From a website attacking the carnivore diet:
“As mentioned earlier, the lack of plant-based fibers in a carnivore diet may lead to reduced production of short-chain fatty acids (SCFAs). SCFAs are crucial for maintaining a healthy gut lining and reducing inflammation. A decrease in SCFA production can potentially compromise gut health and increase the risk of inflammatory conditions...
...Dysbiosis, an imbalance in the gut microbiome, can result from significant changes in diet. A carnivore diet may increase the risk of dysbiosis by reducing the diversity of gut bacteria and altering bacterial metabolism. Dysbiosis has been linked to various health issues, including IBD, obesity, and mental health disorders.”
https://carnivoresdigest.com/carnivore-diet-can-impact-your-gut-microbiome/
But...what if SCFAs are “crucial” for healing problems CAUSED by the fiber? After all, many of us can report having less problems with our bowels after going very low fiber. In fact, many report being “healed” of leaky gut and other problems SCFAs are supposed to help.
Many report being CURED of “IBD, obesity, and mental health disorders” after going keto/carnivore.
It is a bit like defining saturated fats as “bad” and then saying eating lots of meat is bad because it has saturated fats. Circular reasoning.
Define “good bacteria” as bacteria that digests fiber, and fiber becomes “essential”. Yet in the real world...many of us almost never eat fiber and have zero issues.