Psyllium husks and seeds contain high levels of fibre (the mucilage) and swell becoming highly gelatinous when moistened. By absorbing water and maintaining a high water content within the large bowel they increase the bulk of and soften the stool, easing its passage.

The soluble fibre in psyllium has also been shown to help lower cholesterol. Studies have shown psyllium can lower total as well as LDL ("bad") cholesterol levels, which may help reduce the risk of heart disease.

Studies suggest that psyllium as part of a high fibre diet may help lower insulin and blood sugar levels and improve cholesterol levels in people with type 2 diabetes. It may also reduce the chance of developing diabetes in those who are at risk.