Digestion Supplement Guide: What The Evidence Shows

Almost everyone reaching for a digestion supplement is trying to fix one of three things: going less often than they would like, feeling heavy or bloated after eating, or a general sense that things are sluggish. Those are different problems with different answers, and the aisle mostly sells one kind of bottle for all three.

It is worth being blunt about the first thing that moves any of them, because no capsule outperforms it. Water, fibre from food, movement and a regular eating pattern shift the same symptoms, cost nothing, and are the comparison any supplement is actually competing against.

What a supplement can add is convenience and concentration. A heaped tablespoon of psyllium husk stirred into water is unpleasant enough that many people stop; a capsule is not. That trade is real, and understanding it is the difference between buying sensibly and buying hopefully.

Four reasons people buy, and how much the published record supports each purchase.

Psyllium husk, from Plantago ovata, has the best claim on a reader's attention in this category. Rao and Brenner's systematic review of over-the-counter constipation therapies grades it at moderate evidence, grade B, which puts it behind polyethylene glycol and senna and ahead of most of what sits beside it on a shelf.

The mechanism is unglamorous and well understood. Psyllium is a soluble fibre that holds water, which increases stool volume and softens it. That is why taking it with a full glass of water is not a nicety, and why the pharmacobezoar literature exists for people who took bulking fibre without enough fluid.

The number that matters is the dose, and it is a large one.

Five records, and every one of them sits in grams rather than milligrams.

That last row is the one to carry away. The pooled analysis found the effect emerging above 10 grams a day, which is roughly a heaped tablespoon of husk. A capsule holds a fraction of a gram of everything it contains put together.

This is not an argument that a capsule containing psyllium is useless. It is an argument that a capsule containing psyllium is not the same purchase as the trials, and that a label printing a fraction of a gram should not be read as though it were. Psyllium also has a second literature, on LDL cholesterol at a median of about 10 g a day, and a third, on body weight across twenty-two trials, which found no significant effect.

Four plants turn up repeatedly on digestion panels and belong to one chemical family: cascara sagrada bark, aloe leaf, Chinese rhubarb root and buckthorn bark. All four carry anthraquinones, and anthraquinones are stimulant laxatives. They act on the bowel wall rather than on the stool.

The first thing to say is that they do something. That is exactly why they need handling. A person who takes a stimulant botanical and notices an effect within a day or two has not proved that a blend is well formulated; they have proved that stimulant laxatives work, which was never in doubt.

The second thing is the time limit. van Gorkom's review of the class concludes that short-term use is generally safe and that long-term use cannot be recommended. Nascimbeni's work measured anthranoid laxative use at 32.7 per cent among sigmoid-cancer patients against 8.3 per cent in controls, using aberrant crypt foci as the endpoint. That is an association in an observational design rather than a demonstration of cause, and it is enough to make indefinite daily use an unattractive plan.

Two more records belong here. A case report of cascara-associated intrahepatic cholestasis and the LiverTox monograph describe liver injury in a small number of people, and Guo and Mei's toxicity review records that aloe vera whole-leaf extract is classified by IARC as a possible human carcinogen, Group 2B.

None of that makes these plants unusable. It does make them the wrong basis for a product somebody takes every day for a year, and a label that says nothing about duration is leaving out the most important instruction it could give.

Probiotic evidence is strain-specific and quantity-specific, which makes it the class most often misrepresented on a label. Xie's network meta-analysis compares strains and mixtures against specific outcomes rather than treating probiotics as one thing, and the results differ by strain.

The trials that do exist print two things a label often does not. Martoni's trial of Lactobacillus acidophilus DDS-1 ran ten billion colony-forming units a day for six weeks in 330 adults. Airaksinen's constipation trial used L. acidophilus NCFM at ten billion CFU inside a blend. Both name a strain designation, and both name a count.

A label that prints only the species name has given a reader neither. There is no way to tell whether a capsule holds a researched quantity or a token one, and no way to tell whether the strain is the one that was studied. NCCIH's own summary makes the strain-specificity point directly.

Bentonite is a clay with genuine adsorptive properties, and that chemistry is real. Wang's work measured a high-capacity bentonite binding aflatoxins, which is a study about mycotoxin sorption rather than about bloating or regularity in people.

A search of the human literature for ingested bentonite against digestive symptoms turns up no outcome trial to cite. That is worth saying in exactly those words rather than filling the gap with a mechanism story, because a mechanism story is what most of this aisle offers in place of a result.

There is also a practical consideration a label rarely mentions. An adsorbent binds things indiscriminately, so anything taken near it, including medicine, is a consideration rather than an irrelevance.

The honest position on clays is therefore narrow: interesting chemistry, no human digestive outcome evidence found, and a reason to space it away from anything else being swallowed.

Gentian root has a long European history as a digestive bitter, taken before food on the theory that bitterness prompts secretion. The traditional use is real and old. The modern evidence is where it becomes complicated.

Olennikov's study measured a gastric stimulatory effect in four Siberian gentians: G. algida, G. decumbens, G. macrophylla and G. triflora. Gentiana scabra, which is the species that turns up on supplement panels, is not among the four. The one systematic review of a G. scabra formula studies herpes zoster, which is a different subject entirely.

So a panel naming scabrous gentian is naming a plant with a traditional reputation borrowed from relatives that were actually studied. That is not the same as saying it does nothing. It is saying nobody has shown what it does in people, and a label implying otherwise is reaching.

Alfalfa belongs in the same paragraph for a different reason. A search of the human literature returns plant physiology, wound-dressing materials and animal cholesterol work from the 1980s. What it does return for people is a caution: Brown's review covers the L-canavanine reports connected with lupus, and the underlying chemistry is documented separately. An ingredient with a caution and no efficacy record is an odd thing to find on a digestion panel.

Two more things turn up on these panels often enough to be worth a paragraph each, and both come with a detail that changes what they mean.

Oat carries a real cholesterol literature. Whitehead's meta-analysis of twenty-eight randomised trials ran beta-glucan at 3.0 to 12.4 grams a day, and Ho's analysis and Wolever's multi-ethnic trial sit alongside it. Two things about that literature do not transfer to most supplement panels. It is about cholesterol rather than digestion, and the beta-glucan comes from the grain rather than from oat straw, which is a different part of the plant.

Calcium as calcium carbonate is the commonest passenger of all. Straub's review of forms and doses carries the practical point: carbonate needs stomach acid and is best absorbed with a meal, while citrate suits people with low acid or on acid-suppressing drugs. A panel putting carbonate in a capsule taken away from food has picked the harder combination, usually for a reason to do with the other ingredients.

The general point about passengers is that they are rarely there in a quantity that would matter on their own. A hundred milligrams of calcium against a reference figure of 1,300 mg is a rounding error in a diet, and it is worth reading as one.

Read a dozen of these labels and the same verb appears on all of them. Supports healthy digestion. Supports regularity. Supports gut comfort. That is not a coincidence and it is not evasive writing for its own sake.

A dietary supplement in the United States may make a structure or function claim, which describes an effect on the normal structure or function of the body. It may not claim to diagnose, treat, cure or prevent a disease, because that is a drug claim and a drug claim requires a drug approval. Constipation is a condition. Supporting regularity is a function.

So the word supports is the boundary line, and every bottle sits just inside it. That is why a seller's own sales page is often bolder than its label: the label is a regulated surface and a web page is less so. Where those two disagree, the label is the one that was drafted by somebody who had to be careful.

• Enzymes. Digestive enzyme supplements are a separate literature with its own questions and are not on the panels this guide was written around.
• Prescription treatment. Polyethylene glycol and senna both grade higher than anything here in the same review, and both are worth knowing about.
• Diagnosis. Nothing in this guide can tell anyone why their digestion changed, and a change that is new, persistent or accompanied by bleeding, weight loss or pain belongs with someone who can examine you.
• Individual tolerance. Two people taking the same bulking fibre at the same dose can have entirely different weeks, and psyllium has a reported anaphylaxis case literature of its own.
• Price. A cheaper bottle at a researched dose beats an expensive one below it, and this guide takes no view on any particular ladder.

The last line is worth one more sentence. Bulk psyllium husk costs a few cents a serving and reaches the researched dose without difficulty. It is also unpleasant enough that many people give up on it, which is precisely the gap capsules are sold into. Both halves of that are true at once.