Psyllium refers to the fibres taken from the plant known as "Plantago ovate".
Fibre - the carbohydrate part of plant foods that does not completely digest, resulting in it passing through our stomachs, small-intestines and eventually ending up in our large intestines.
Psyllium is a type of soluble fibre, which means it is water-soluble and gel forming. It is also poorly fermented, meaning our gut bacteria won't turn it into gas (hence, it shouldn't influence bloating and flatulence).
Psyllium is commonly known by the brand name Metamucil.
Psyllium is commonly used as a bulk laxative, which is an agent that has laxative effects secondary to increasing stool size. Compared to majority of other laxatives (e.g. Senna) it is much more gentler on the bowels.
Psyllium bulks stools by increasing water and gas absorption in the small intestines and colon. This in turn gives stools more size (bulks it), as well as softens and lubricates them.
Psyllium has been proven to increase faecal size and moisture, commonly resulting in softer and easier passed stools. Interestingly, it can help both those experiencing loose stools, as well as those with hard stools!
Therefore, relative to other sources of dietary fibre, psyllium appears to be more effective at forming stools and an added benefit... it is one of the few fibres that does not result in excess gas production, meaning it is often well tolerated in those with an irritable bowel (IBS).
Psyllium can be added to porridge, smoothies or other drinks.
It must be consumed with fluid.