Journal September 27, 2026 5 min read

How is intestinal permeability measured?

Intestinal permeability is assessed by tracking the urinary recovery of orally administered probe molecules, most commonly the lactulose-to-mannitol ratio, alongside other sugar, PEG and protein markers.

peptides-pro Editorial

Intestinal permeability is the term for the passive, paracellular and transcellular flux of solutes across the intestinal epithelium. In the research literature it is also referred to as gut barrier function, intestinal barrier integrity, or, when it is impaired, as a "leaky gut" phenotype. It is not a single molecule but a physiological property, and it is therefore quantified indirectly, by measuring how much of an orally administered probe substance reaches the urine or blood unchanged. The most widely used index is the urinary lactulose : mannitol ratio, collected over a defined window after an oral dose; because lactulose is largely excluded by intact tight junctions while mannitol is absorbed transcellularly, a rise in the ratio is read as increased paracellular permeability [6].

The work in this area centres on the tight-junction protein complex — claudins, occludin and the zonula occludens family — which regulates the paracellular pathway, together with the mucus layer and the mucosal immune compartment that sit above it.

Research Studies

Collagen peptide and the lactulose : mannitol ratio in healthy adults

A registered clinical trial has evaluated 45 days of daily collagen peptide at three doses (2.5 g, 5 g and 10 g) against placebo in healthy adults, with intestinal permeability provoked by an acute aspirin challenge. The primary comparison is the change from Day 42 to Day 45 in the urinary lactulose : mannitol ratio, from a 5-hour urine collection [6].

LSCP-I and barrier integrity in Caco-2 cells and murine colitis

A low-molecular-weight collagen peptide fraction (LSCP-I, under 3 kDa) derived from Lutjanus erythropterus scales was tested in Caco-2 cell monolayers under macrophage-mediated inflammatory injury and in murine colitis models. At 50 µg/mL in the cell model, the fraction increased proliferation by 35% and migration by 40%, preserved barrier integrity, reduced reactive oxygen species by 45% and lipid peroxidation by 30%, and restored glutathione and superoxide dismutase [1]. These findings are from cell culture and animal models, not from human studies.

Oral glutamine and sex-dependent permeability in diet-induced obesity

Male and female C57BL/6 mice received a standard or high-fat diet (60% kcal from fat) for 14 weeks, with oral glutamine in drinking water (2 g/kg/day) from week 12. Body composition, glucose tolerance, insulin sensitivity, intestinal permeability and colon outcomes were characterised, and the metabolic and gut responses to glutamine differed between the sexes [2]. This is a mouse study; the sex-specific pattern has not been established in humans.

Zein-based nanoparticles and peptide permeability in Danio rerio

Hybrid zein–Eudragit RS100–chitosan nanoparticles were developed for oral co-delivery of insulin and liraglutide, with the aim of protecting both peptides from enzymatic degradation and supporting absorption across the intestinal barrier. The particles measured approximately 230 nm with a polydispersity index below 0.1 and a zeta potential of about +46 mV, and were predominantly amorphous by FTIR, XRD, TGA and DSC. Preliminary in vivo evaluation was performed in Danio rerio [3].

Exercise and permeability in elite rowers

An observational study of thirty Polish Youth National Rowing Team members aged 19–24 is assessing multilevel physiological, molecular, metabolic, intestinal, immunological and psychophysiological responses to rowing-specific exercise, including maximal and prolonged ergometer efforts, with intestinal permeability among the integrated endpoints examined across two training periods [4].

Synbiotic sugar product and intestinal health in overweight adults

A randomised, double-blind, controlled crossover study is testing a sugar-based synbiotic containing inulin and Bacillus coagulans BC30 spores in healthy overweight participants. Twenty participants complete a 2-week run-in and two 4-week intervention periods separated by a 4-week washout, receiving either the synbiotic (1 × 10⁹ CFU/day) or a matched control sugar product with inulin but no spores; the primary outcome is change in fasting markers of subclinical inflammation, including high-sensitivity C-reactive protein [5].

Fiber supplementation and permeability in alcohol use disorder

A clinical trial is testing whether a fiber-enriched diet high in inulin and pectin, added to standard care, reduces intestinal permeability in patients with alcohol use disorder aged 19–65. The stated hypothesis is that fiber-driven changes in the gut microbiota and its metabolites will lower permeability and improve abstinence, craving, anxiety, inflammation, steatosis and hepatic fibrosis [7].

Akkermansia muciniphila, berberine and barrier integrity in shift workers

A study in night-shift workers is examining Akkermansia muciniphila and berberine supplementation in relation to insulin sensitivity. The rationale cites the association of A. muciniphila with maintenance of intestinal barrier integrity and the reported upregulation of the bacterium by berberine [8].

Permeation enhancers and epithelial transport of a PROTAC

Work in rats has examined how intestinal permeation enhancers affect solubilisation and epithelial transport of the PROTAC ARV-471, a molecule whose properties fall outside rule-of-five chemical space and which shows poor intestinal solubility, permeability and absorption [9].

Natural products and NSAID-induced small intestinal injury

A systematic review assessed natural products, functional foods and probiotics for preventing or treating NSAID-induced small intestinal injury, a complication among chronic NSAID and aspirin users, with mechanistic consideration of oxidative stress and microbiome modulation [10].

Permeability in PCOS and in indomethacin-induced ulcer models

A review of diagnostic and prognostic biomarkers in polycystic ovary syndrome examines insulin resistance, systemic inflammation and endometrial receptivity [11], while a preclinical study of canagliflozin in indomethacin-induced peptic ulcer reports effects on inflammation, pyroptosis, autophagy and gut integrity [12].

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