Dietary fibre and psyllium.

Different fibres, different effects

Soluble fibres attract water and can form a gel; some have evidence for lowering cholesterol. Insoluble fibres add bulk to stool and help food move through the digestive system. Foods commonly contain mixtures, so the effect depends on the fibre and the outcome being measured.1

Food and psyllium

Fibre is found in foods such as beans, vegetables, fruit, whole grains, nuts and seeds. Psyllium is used as a bulk-forming laxative and is also available in fibre products. A result for one fibre or product should not automatically be transferred to another.12

Can psyllium lower cholesterol?

Psyllium is a soluble fibre that forms a gel in the gut. In a 2018 review of 28 randomized trials involving 1,924 participants, people assigned psyllium had lower LDL cholesterol—a blood marker associated with cardiovascular risk—than comparison groups on average. The estimated average difference was 0.33 mmol/L lower, but individual results varied and the reviewers rated the LDL evidence moderate because of inconsistency. The studies measured blood markers, not whether each participant had a heart attack or stroke, and the findings do not establish the effect of every fibre product. Psyllium is not a substitute for prescribed cholesterol treatment. Ask a clinician or pharmacist how a specific product fits with medicines and individual circumstances.3

Can psyllium help irritable bowel symptoms?

Irritable bowel syndrome (IBS) involves recurring abdominal pain and changes in bowel habits. In a Dutch primary-care trial, 275 adults with IBS were assigned psyllium, wheat bran or a rice-flour placebo for up to three months. Among people assessed in the first month, 45 of 79 taking psyllium reported adequate relief for at least two weeks, compared with 27 of 78 taking placebo. By the third month, the difference between psyllium and placebo was not statistically significant. Many participants did not complete the study, which makes longer-term results harder to interpret; the results do not predict how an individual will respond. More people left the bran group early, often because symptoms worsened. The Dutch health research organisation ZonMw funded the study, and Pfizer supplied the psyllium. Psyllium can cause bloating and requires adequate liquid: follow the specific product instructions and discuss persistent or changing symptoms with a clinician rather than assuming IBS. For a different approach, see the evidence on probiotics for IBS.42

Practical safety

Psyllium products must be taken with adequate liquid according to their instructions; insufficient liquid can cause choking. Difficulty swallowing, intestinal blockage, relevant medicines or other health conditions require professional advice. Changes in fibre intake can also cause gas or bloating. The US MedlinePlus psyllium guidance names digoxin, salicylates such as aspirin, and nitrofurantoin as medicines that should not be taken within three hours of psyllium. Ask a pharmacist about your exact products and other medicines; do not stop a prescribed medicine on your own.

US MedlinePlus guidance advises against taking psyllium for more than one week unless a doctor directs it. Before using it, discuss diabetes, heart or kidney disease, high blood pressure, rectal bleeding, pregnancy or breastfeeding with a clinician. Avoid breathing in psyllium powder when mixing it, as inhalation can cause an allergic reaction.12