Table 2

Summary of the literature on conditions that result in stress to the intestinal barrier, with documented effects on intestinal permeability or biochemical evidence of mucosal damage, and restoration with a dietary, non-pharmacological intervention

Barrier stressor; clinical scenario	Specific study	Effects on barrier function		Dietary intervention and its effects	Reference #
Barrier stressor; clinical scenario	Specific study	Intestinal permeability	Mucosal damage	Dietary intervention and its effects	Reference #
Endurance exercise Marathon runners with faecal occult blood or bloody diarrhoea	Biking challenge	Urine iohexol (MW 821 Da) ↑	Serum I-FABP ↑, zonulin ↓		70
	Running challenge	LRR ↑ and correlated with core temperature (eg, >39°C)	ND		71
	Biking challenge	LRR ↑	Serum I-FABP ↑	Citrulline (vs alanine) reversed ↑serum I-FABP and gastric hypoperfusion without effect on LRR.	72
	Biking challenge	ND	Serum I-FABP ↑	Sucrose (vs nitrate) reversed ↑ serum I-FABP no Δ gastric hypoperfusion.	73
	Seven runners, two boxers, three rugby	LRR ↑	ND	Nurticeutical colostrum versus placebo reduced LRR ↑ and apoptosis of cell lines in vitro.	74
NSAID enteropathy: NSAIDs cause small bowel ulcers and inflammation	Diverse NSAIDs, for example, indomethacin	⁵¹CrEDTA and saccharides	ND		75–77
	Indomethacin	LRR ↑	ND	Zinc carnosine (vs placebo) reduced LRR and increased HT29 cell proliferation (vs ZnSO4).	78
	Aspirin	increased colon permeability: urine SLR and sucralose	ND	Bifidobacterium BB-12 and adolescentis (IVS-1) and galacto-oligosaccharide prebiotic reduce colon permeability.	79
Pregnancy with or without obesity		Increased serum zonulin and increased serum LPS, associated with metabolic risk markers.	ND		80
		High serum zonulin.	ND	n-3 PUFAs, fibre and a range of vitamins and minerals: reduced high serum zonulin; greater richness of gut microbiota.	81
		No effects on serum zonulin or LPS.	ND	Probiotics and/or LC-PUFA.	82

Da, dalton; I-FABP, intestinal fatty-acid binding protein; IVS-1, first intervening sequence; LC-PUFA, long chain polyunsaturated fatty acids; LPS, lipopolysaccharide; LRR, lactulose rhamnose ratio; MW, molecular weight; ND, not determined; NSAIDs, non-steroidal anti-inflammatory drugs; PUFA, polyunsaturated fatty acids; SLR, sucralose-to-lactulose ratio.