A daily system, not a rescue button
Fibre is often noticed only when digestion feels off. That makes it sound like a rescue ingredient. A better view is daily system design. Fibre changes water handling, stool structure, microbial substrate, meal texture, viscosity, and the physical work of eating.
Different fibres do different jobs. Wheat bran, psyllium, legumes, resistant starch, fruit pectin, vegetable structure, and gums cannot be reduced to one word. Some add bulk. Some form gels. Some ferment. Some change mouthfeel. That is why the better question is not whether fibre fixes one problem. It is whether the everyday diet gives the gut enough useful material to work with.