The fraction of dietary fibre that does not dissolve in water and resists digestion in the human gut. Found abundantly in wholemeal bread, bran, brown rice, and the skins of fruits and vegetables, insoluble fibre consists mainly of cellulose, hemicellulose, and lignin. It adds bulk to the stool and speeds the passage of material through the intestines, helping to prevent constipation and maintain bowel regularity. Unlike soluble fibre, it contributes little to fermentation by gut bacteria and has only modest effects on blood cholesterol or glucose. A diet rich in insoluble fibre is associated with lower risk of diverticular disease. Nutrition guidelines recommend a mix of both fibre types, typically from whole grains, vegetables, and legumes.