Psyllium Fibre

Claimed to lower LDL cholesterol, improve glycaemic control, relieve constipation and IBS, promote satiety and weight loss, and feed the microbiome. The lipid evidence is the most internally coherent in this whole dataset: across 28 trials and 1,924 participants, LDL cholesterol fell 0.33 mmol/L (95% CI −0.38 to −0.27), non-HDL cholesterol 0.39 mmol/L and apolipoprotein B 0.05 g/L, three correlated targets moving together with tight confidence intervals. For scale, a moderate-intensity statin lowers LDL-C roughly three to five times as much. It also holds one of the few FDA-authorised — not merely qualified — health claims available to a supplement ingredient.

The glycaemic effect scales with how abnormal the starting point is. The manufacturer-authored analysis is titled, explicitly, "psyllium fiber improves glycemic control proportional to loss of glycemic control": in type 2 diabetes it reports fasting glucose −37.0 mg/dL and HbA1c −0.97%, with no comparable effect in euglycaemic subjects. The independent, university-funded counterpart finds a substantially smaller HbA1c effect, −0.75% (95% CI −1.21 to −0.29) at moderate certainty. A person with normal glucose and normal LDL should not expect either set of numbers.

The principal documented harm is choking and oesophageal or gastrointestinal obstruction if taken without adequate fluid — serious enough that US labelling law mandates a capitalised choking notice, which is a stronger safety statement than any efficacy claim carried by most supplements. Other effects are gastrointestinal: bloating, flatulence, cramping. No hepatotoxicity signal.