The indigestible portion of plant foods (e.g., cellulose, lignin, chitins, pectins) that pushes food through the digestive system, absorbing water and easing defecation. Potential advantages of consuming fiber are the production of health-promoting compounds during the fermentation of water-soluble fiber by bacteria, and insoluble fiber's ability (via its passive water-attracting properties) to increase bulk, soften stool and shorten transit time through the bowel (‘intestinal tract’).