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AN-PEP (Prolyl Endopeptidase)
An oral enzyme from the mould Aspergillus niger that breaks down gluten in the stomach. Small trials show it lowers the gluten reaching the small intestine after a meal, but it is not a treatment for coeliac disease and does not make gluten safe for people with coeliac disease to eat.
What the evidence says
Most AN-PEP studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from medium-quality randomised trials published 2006–2025 with a typical study size of 18 participants.
Based on 11 studies · 4 RCTs · 114 total participants
Confidence
Moderate confidenceBy outcome
Emerging 3.5: two small placebo-controlled crossover trials (12 and 18 people) consistently show the enzyme degrades most gluten in the stomach, but that is a surrogate measure. The trials in coeliac disease missed their primary endpoints, the 40-person randomised trial found no difference from placebo in stool gluten peptides, and no trial shows a clinical benefit such as protected intestinal lining or fewer symptoms against placebo.
AN-PEP is a prolyl endopeptidase produced by the mould Aspergillus niger. Gluten is rich in the amino acid proline, which makes parts of it resistant to human digestive enzymes, and in coeliac disease those surviving fragments trigger the immune attack on the small intestine.
This enzyme cuts protein chains next to proline, works at stomach acidity and resists pepsin, so it can break gluten down in the stomach before it reaches the small intestine.
In two small crossover trials, one in 12 healthy volunteers and one in 18 people who reported gluten sensitivity, it sharply reduced the gluten measured in the stomach and duodenum after a gluten-containing meal.
The trials in coeliac disease did not show protection: a 16-person pilot could not show any effect on the intestine, and a 40-person randomised trial found no difference from placebo in gluten peptides in stool. A study of enzyme-treated bread found no symptom benefit in people with self-reported gluten sensitivity.
It is NOT a treatment for coeliac disease and must not be used to eat gluten. A strict gluten-free diet remains the only established treatment.
Its most defensible use is as an extra layer against accidental or trace gluten in people who already avoid gluten, and even that rests on gluten measurements in small, short studies rather than on clinical outcomes.
Cleaves protein chains next to proline, breaking down the proline-rich gluten fragments that human digestive enzymes leave intact, including the fragments coeliac T cells react to.
Works best at pH 4-5, stays stable at pH 2 and resists pepsin, so it can act in the stomach before gluten reaches the small intestine.
In laboratory models other food proteins and baked gluten slow its action, so the amount of gluten it can clear depends on the meal.
Not a treatment and not a licence to eat gluten. Keep a strict gluten-free diet. Trials did not show protection of the intestine, and it can at most be considered as an extra layer against accidental exposure, after discussion with your gastroenterologist.
Not studied. Do not rely on it to prevent an allergic reaction to wheat.
It reduces gluten in the stomach, but no trial shows that it reduces symptoms.
Not studied. Ask a clinician or pharmacist before use.
Not studied in children.
Tip: Avoid with a known mould or fungal-enzyme allergy
AN-PEP has an evidence score of 3.5/10 — emerging evidence based on 11 indexed studies. An oral enzyme from the mould Aspergillus niger that breaks down gluten in the stomach. Small trials show it lowers the gluten reaching the small intestine after a meal, but it is not a treatment for coeliac disease and does not make gluten safe for people with coeliac disease to eat. Representative study: PMID 38617446.
Dosing for AN-PEP: Taken at the start of a meal that may contain gluten. The longest trial gave two 325 mg capsules (about 70% enzyme preparation) with each of three meals a day for 4 weeks. Products label strength in enzyme activity units that are not comparable across brands, and no trial defines how much enzyme clears a given amount of gluten. Individual needs vary, so check the right dose for you with a healthcare provider.
The best time to take AN-PEP is with meals. Take it with food. The enzyme acts on gluten in the stomach, so it has to be there at the same time as the food.
AN-PEP has a moderate safety rating: most adults tolerate it at the studied doses, but there are precautions worth knowing. Reported side effects include allergic reaction in people sensitised to Aspergillus or fungal enzymes. How often they occur is not established for all of them. Use caution if any of these apply to you: Using it in order to eat gluten with coeliac disease: it is not a treatment for coeliac disease and does not make gluten safe; Known allergy to Aspergillus moulds or fungal-derived enzymes.
Lactase
Too few graded studiesA digestive enzyme taken with dairy to break down lactose. Small placebo-controlled challenge trials mostly show less breath hydrogen and, in most, fewer symptoms in people with lactose malabsorption, but responses vary widely between people and products and no pooled analysis in adults exists.
Digestive Enzymes
Too few graded studiesEnzyme blend that helps break down proteins, fats and carbohydrates. Small trials suggest less discomfort in functional dyspepsia, but the evidence for everyday bloating is mixed.
Oral Proteolytic Enzymes
Too few graded studiesCombinations of protein-cleaving enzymes (trypsin, chymotrypsin, papain, bromelain), often with rutoside, taken between meals for joint pain and swelling. In osteoarthritis they were non-inferior to diclofenac in two 6-week trials designed to test that, and a pooled reanalysis reported fewer adverse events than diclofenac, but placebo-controlled evidence is mixed and a 721-person ankle sprain trial found no benefit.
Diamine Oxidase (DAO)
Too few graded studiesAn oral enzyme, usually from pig kidney or pea sprouts, taken just before meals to break down histamine from food in the gut. Small trials in people with suspected histamine intolerance report fewer symptoms, but the trials in migraine, urticaria, fibromyalgia and insomnia mostly failed to show a clear difference from placebo.
Reviewed by Dr. Baher Al Hakim · Last reviewed October 2026 · evidence from 11 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.