Provided is a use of fibers formed of β-1-4-glucan in manufacturing a composition for preventing or treating diarrhea, constipation or irritable bowel syndrome, wherein the fibers have a diameter between 15 nm to 35 nm and a mean length of between 1.5 μm and 3.5 μm. Also provided is a method for preventing or treating diarrhea, constipation or irritable bowel syndrome with the fibers formed of β-1-4-glucan.