Fermentation in the gut is not the same as fermentation in a dosa batter, but the idea is related.
When certain fibres reach the large intestine, gut bacteria can ferment them. During this process, they produce short chain fatty acids, mainly acetate, propionate and butyrate. These compounds are part of why prebiotic fibre is discussed in gut health and microbiome nutrition.
Different fibres ferment differently. Inulin and FOS may ferment quickly and cause gas for some people. Resistant starch may ferment in another way. Acacia fibre and PHGG are often used for gentler daily support. Psyllium husk is less fermentable and more known for gel formation and water holding.
Indian food gives many fermentation inputs: dal, chana, rajma, vegetables, fruits, oats, millets, raw banana flour and cooked and cooled starches. But increase gradually. A sudden jump in beans, sprouts and prebiotic supplements can create discomfort.
Short chain fatty acids are not something you need to measure at home. They are a useful way to understand why fibre is not only about stool bulk.
Fibre feeds bacteria. Bacteria produce metabolites. The gut routine is the daily connection between the two.
Fermentation is not a side effect to manage around. It is the reason a fibre rich diet does more for the gut than bulk alone ever could.