Methodology

Scoring rubric

Each product is scored 0 or 1 on each of six criteria. No weighting, no partial credit. Maximum score: 6.

How criterion 2 is applied

Criterion 2 applies only where potency depends on a marker compound: standardized herbal or botanical extracts (e.g., % withanolides, % curcuminoids). Products containing no such ingredient are not penalized for its absence. Criterion 2 scores 1 by default when nothing in the formula requires a stated percentage.

What counts as standardization-dependent. Criterion 2 applies wherever a stated percentage is required to compare the label to a reference range — not only to botanical marker compounds. An ingredient sold at graded purities, such as xylooligosaccharide (marketed anywhere from roughly 35% to 95% XOS), declared only as an extract weight cannot be compared to a range expressed in the active compound. The percentage is therefore potency-determining and its absence scores 0. The test is functional: if the disclosed figure cannot be converted into the unit the evidence uses, the standardization is missing.

Unlike the probiotic exclusion under criterion 4, this is not a unit-mismatch problem; the requirement simply does not apply. The criterion therefore remains a scored point rather than reducing the total possible score, keeping every product comparable on the same 6-point scale.

How criterion 3 is applied

Criterion 3 asks whether the specific chemical form is named, because the form determines what the body actually receives. "Magnesium glycinate" scores 1; "magnesium" scores 0.

Probiotics. The equivalent of chemical form for a live microorganism is the strain designation. Probiotic effects are strain-specific and do not generalize across a species: Lactobacillus rhamnosus GG has been trialled for outcomes that other L. rhamnosus strains have not, and evidence for one Bifidobacterium longum strain is not evidence for another. A label naming only genus and species does not identify what is in the bottle, and the published literature cannot be matched to it.

Criterion 3 therefore scores 1 for a probiotic product only when every listed organism carries a strain designation — for example Lactobacillus rhamnosus GG or Bifidobacterium longum 35624. Genus and species alone — "Lactobacillus acidophilus" — scores 0, and a single undesignated organism anywhere in the formula is enough to score 0. A strain designation means a specific identifier assigned by a culture depositary or the manufacturer, not a marketing name for a blend.

This rule governs the criterion 3 point only. Probiotics remain excluded from criterion 4 for the separate unit-mismatch reason given below.

How criterion 4 is applied

Clinical dose ranges are outcome-specific. Glutamine trials measuring intestinal permeability and glutamine trials measuring IBS symptom severity used different doses; zinc carnosine trials for permeability and for gastric ulcer healing used different doses. There is no single "clinical dose" for most ingredients.

Criterion 4 is therefore scored against the outcome the product claims on its label or product page. A product marketed for intestinal permeability is scored against permeability trials. A product marketed for symptom relief is scored against symptom trials.

Where the literature is contested, the reference table records the range and the disagreement in the notes field, and the product is given the benefit of the doubt: falling within any credible published range for the claimed outcome scores 1.

Where no adequate human trial exists for an ingredient at all, that ingredient is marked "no adequate human trial identified" and excluded from the product's criterion 4 assessment. A product scores 0 on criterion 4 only if at least one of its actives has a reference range and falls outside it.

Human trials only. Animal and in vitro studies are excluded from the reference table. Criterion 4 requires published human-trial evidence for the claimed outcome. An ingredient with substantial preclinical support but no human trial is treated as having no reference range.

Positive-outcome trials only. Reference dose ranges are drawn from trials that found a significant effect on the outcome measured. Trials that found no effect are recorded in the notes field but do not set the range. A dose shown not to work is not evidence that the dose is correct.

Negative findings carry their search. "No adequate human trial identified" is a claim about the literature, and it is what excludes an ingredient from criterion 4 — so a wrong one silently spares a product a point it should have lost. Rows making that claim record the date the search was run and what it returned, the same standard criterion 5 applies to a missing certificate. Absence of evidence is recorded as of a date, not asserted in general.

Absorption enhancers. Ingredients included to increase the bioavailability of other ingredients rather than to produce an independent effect are excluded from criterion 4. Their doses are recorded in the reference table where trials state them, but no trial tests them against the outcome the product claims.

Evidence hierarchy. Where more than one trial could set a range, they are not equal. Two rules apply, in order, after the human-trials-only and positive-outcome-only rules above:

1. Attribution. A trial of a multi-ingredient formula cannot set a range for any single component, because the effect cannot be attributed to that component. This already governs the multi-herb blends in the reference table, and it applies identically to a finished commercial product: a synbiotic trialled whole does not establish the dose of its prebiotic.
2. Independence. Where an independent trial of the ingredient exists, it sets the range. A trial authored or funded by the manufacturer of the ingredient or product is recorded in the notes, and sets a range only where no independent trial does — flagged in the row as the weaker basis.

Without the first rule a brand could establish its own dose by trialling the formula rather than the ingredient; without the second, by funding the only study. Both would let the audited party set the standard it is audited against.

Probiotics. Clinical trials of probiotic strains report dosing predominantly in milligrams of preparation rather than colony-forming units, while product labels almost universally report CFU. These units are not reliably interconvertible, as CFU per milligram varies by manufacturer and by viability at manufacture versus expiry. Probiotic ingredients are therefore excluded from criterion 4 and assessed on criteria 1, 2, 3, 5 and 6 only.

How criterion 5 is applied

Criterion 5 asks whether a third-party certificate of analysis for the product is publicly accessible: reachable without an email address, an account, or a support request. A batch-number lookup that returns a certificate scores 1, provided no email or account is required to use it.

Three things are not a certificate of analysis:

• A "third-party tested" claim, badge, or seal with no document behind it. The criterion is about the document being accessible, not the claim being made.
• A GMP or facility registration certificate, which covers the manufacturing site rather than the product.
• A certificate issued by the manufacturer's own laboratory, which is not third-party.

A zero is a negative finding and is recorded as one. The search covers the product page, the brand site (footer links commonly named Quality, Testing, Lab Results, Transparency, or Certificate of Analysis), a site-scoped web search for "certificate of analysis", and the retail listing's images. Where that search returns nothing, the row records that no publicly accessible certificate was located on the capture date — not that none exists. A certificate published later, or reachable by a route this search did not cover, would change the score, and the dated record makes that revision auditable rather than silent.

Criteria deliberately excluded

The following were considered and rejected as scoring criteria:

• Use of branded or trademarked ingredients. Would reward marketing spend rather than transparency. A product using generic ashwagandha at a clinically studied dose scores identically to one using a branded equivalent.
• Price or value. Not a transparency measure.
• Taste, packaging, brand reputation. Subjective.

Sample selection

The top 30 gut-health supplements ranked in Amazon Best Sellers in Probiotic Nutritional Supplements, captured on 09/05/2026. This list is fixed at capture and not revised as rankings change afterward.

A product is included only if the digestive/gut-health benefit is the first-listed claim in its product title or primary bullet. Products whose first-listed claim is vaginal/urinary tract health, oral/dental health, or an unrelated function (e.g., pre-alcohol support) are excluded, even if digestive support is mentioned secondarily. This test is applied to every product in the category ranking, in rank order, without exception.

What "first-listed" means. The test asks whether the product is presented as a gut-health product, not how a marketing string is punctuated. Where a title opens with a compound benefit phrase naming several systems together — "Immune, Digestive & Gut Health" — digestive health counts as first-listed. A product is excluded only where the first benefit named is wholly unrelated to the gut and digestive support appears later as a secondary claim. The listed exclusions are the guide: vaginal or urinary tract health, oral or dental health, and unrelated functions such as pre-alcohol support are products that are fundamentally about something else, which is what this test is for.

What "top 30" counts. The sample is the first 30 rows of the category ranking as captured, examined in rank order. Exclusions are not backfilled from further down the ranking: a captured boundary is only fixed if it does not move with the number of products that fail the test. The scored set will therefore be smaller than 30.

The captured ranking is recorded in sample.csv, one row per product in rank order, carrying the first-listed claim the test was applied to, the include/exclude decision, and the reason for every exclusion. Excluded products stay in the file: a sample is only auditable if the rejections are visible alongside the acceptances. Without this file the claim that the list was fixed at capture cannot be checked by anyone, including its author.

Data sources

Primary: the NIH Office of Dietary Supplements Dietary Supplement Label Database (DSLD).

Important limitations of DSLD, stated openly:

• Manufacturer submission is voluntary, so coverage is incomplete.
• The database contains both on-market and off-market products.
• NIH does not verify that label information conforms to FDA requirements.

Accordingly, every scored product is verified against its current live label, captured by screenshot with a capture date recorded. Where the live label differs from the DSLD record, the live label governs and the discrepancy is noted in the dataset.

Products that cannot be verified against a current label are excluded from scoring.

Label captures are stored in captures/, named <brand>-<product>-<view>-<YYYY-MM-DD>.png, where <view> is panel for the Supplement Facts panel or listing for the product page carrying the claims that criterion 4 is scored against. Both views are captured for each product, and the same date is recorded in the capture_date field of the row that cites them. A scored row without a corresponding capture is incomplete, not merely undocumented.