These are not great sources. Your first link is mostly anecdotes and doesn't differentiate between "necessary" and "sufficient". No one is claiming that fiber a

These are not great sources. Your first link is mostly anecdotes and doesn't differentiate between "necessary" and "sufficient". No one is claiming that fiber alone will solve all of your health problems. There are also many types of fiber, even within the 'soluble' and 'insoluble' categories, with different properties. You likely have a point since anything in excess can be harmful, but those references don't really support. One thing to keep in mind is that you shouldn't switch diets drastically - you can't expect your low fiber/high sugar microbiota to be able to handle a large dose of fiber all at once. Think of your microbiota as something you need to cultivate. By the way, there's increasing evidence that in the absence of fiber your gut bacteria resort to chewing back your own mucus, whereas if you give them some complex fiber to chew on they leave you alone (https://sci-hub.tw/10.1080/19490976.2018.1513765 https://sci-hub.tw/10.1080/19490976.2018.1513765). This is temporary however and in the absence of fiber you can maintain barrier function if you simply make more mucus. But that requires more energy so you probably have to eat more. Everything has tradeoffs. And other that just giving you the farts, many byproducts of fermentation like short-chain fatty acids (i.e. butyrate, propionate), are able to keep other bacteria at bay while simultaneously feeding your colon cells and keeping them in a non-inflamed state (https://sci-hub.tw/10.1038/s41579-019-0213-6 https://sci-hub.tw/10.1038/s41579-019-0213-6 [Box 3]).