Inulin

A soluble fibre that chicory root and Jerusalem artichoke tubers use to store energy — long chains of fructose that human enzymes cannot break. It is the bulk of the tuber: one analysis put Jerusalem artichoke powder at 70% inulin by dry weight.

Inulin is a chain of fructose units joined by beta-(2,1) bonds. No human digestive enzyme has the shape to cut that bond, so it travels the length of the small intestine untouched and arrives in the colon intact, where Bifidobacterium and a few other genera can ferment it. They produce short-chain fatty acids — acetate, propionate, some butyrate — and the colon becomes slightly more acidic, which is the measurable part of the prebiotic effect. The gas is not a side effect of some other process; it is the same process. Fermentation makes hydrogen and carbon dioxide, and how much you make depends on which bacteria you happen to be carrying. Nobody can yet predict from the outside who gets the benefit quietly and who gets the bloating.

Passes through the small intestine undigested and is selectively fermented by gut bacteria, Bifidobacterium in particular. Studied for bowel function; at 12 g a day, native chicory inulin carries an authorised European claim for maintenance of normal defecation.

Men who want the digestive area covered lightly in one capsule and who tolerate fibre without trouble. Not for anyone with IBS who already reacts to fructans, anyone with hereditary fructose intolerance, or anyone who has had an allergic reaction to inulin. If you are chasing the bowel-function dose, this is the wrong format to get it from.

As the label directs, with water, with or after food. If you are also taking a fibre powder or eating a lot of onions, leeks and wheat, count the fructan load across all of it and raise the total slowly over a couple of weeks — sudden increases cause the wind, not the fibre itself. One useful pairing: in the Gunn trial, taking psyllium alongside inulin cut inulin's gas production back to placebo levels, so if you take BOTTOM LINE's psyllium sachet as well, that is the helpful order of things rather than a clash. The authors called it worth further study, not settled. No known interaction that requires separating inulin from medication.

At a capsule's worth, nothing you will notice — no bowel change, no extra wind, nothing in the mirror. At the doses trials use, 12 g and up, expect stool frequency to shift over two to four weeks and expect to hear about it while your gut adjusts. If you do feel something from SETTLE, the cider vinegar or the enzymes are the likelier cause.

Nagy and colleagues (Critical Reviews in Food Science and Nutrition, 2023; online 2022) pooled 50 randomised trials and 2,525 participants: chicory-derived inulin-type fructans at 3–20 g a day raised Bifidobacterium abundance, standardised mean difference 0.83 (95% CI 0.58–1.08). The same review found the effect in healthy people and in populations with health impairments — except those with gastrointestinal disorders — and found bowel-function benefits in healthy subjects. EFSA's 2015 opinion, authorised as Commission Regulation (EU) 2015/2314, accepted from six studies in 86 subjects that 12 g a day of native chicory inulin (mean degree of polymerisation of 9 or above) contributes to maintenance of normal defecation by increasing stool frequency. Tolerance is documented just as carefully: Gunn and colleagues (Gut, 2022) gave 20 g of inulin to 19 people with IBS in a four-way crossover and measured colonic gas by MRI at a median AUC of 3,145 mL·min, the largest rise of any arm; co-administering 20 g of psyllium cut it to 618 and was no longer different from placebo. Allergy is rare but real — Gay-Crosier and colleagues reported anaphylaxis to inulin in the New England Journal of Medicine in 2000. Not supported: weight loss of any stated amount, glycaemic control at capsule doses, and any treatment of IBS, constipation or bowel disease.