Gut hyperpermeability

There are four layers of protection in the gut:

Improve

• Fiber: bacteria within the gut can feed on the mucus layer particles if there is not enough fiber in the diet, so eating enough fiber helps maintain a thick mucus layer. Also, fiber maintains healthy microbes in the gut. Inulin has been found to be especially effective.
• Short Chain Fatty Acids (SCFAs): these are fermentation products of fiber by gut bacteria and become food for colonocytes (=better barrier in the large intestine) and there’s a positive effect on gut immune cells, too. Studies show that taking SCFAs as supplements is not helpful, so getting enough fiber in the diet is needed.
• Vitamin D: most studies have been done in animals. There are Vitamin D receptors in the gut and vitamin D binds to them with anti-inflammatory effects. Vitamin D is a necessary nutrient of which many people don’t get enough, and so taking a supplement that covers the body’s daily need is a good idea. This is at least 400 IU or 10 mcg per day.
• Vitamin A: Permeability improved with supplementation in children with deficiency. So, make sure to get enough vitamin A every day – good sources are carrots, sweet potatoes, bell peppers, leafy greens etc.
• Zinc: together with vitamin A it improved permeability in Brazilian children with poor growth. Good sources are meat, legumes, seeds, nuts, and dairy.
• Polyphenols: studies show decreased permeability, production of more barrier promoting proteins, and anti-inflammatory effects. Could be because of their beneficial effects on the gut microbiota
• Glutamine: amino acid that is used as fuel by cells lining the intestines. A study in people with IBS-D showed improved permeability with glutamine supplementation of 5 g three times daily for 8 weeks. 
• Probiotics: Lactobacillus reuteri increases butyrate production (a SCFA) and gut barrier integrity by greater production of barrier promoting proteins. S. boulardii was seen to be beneficial in animal models. VSL#3, a combination probiotic prevents decreased barrier protein production in mice. The evidence is promising but much more is needed before conclusions can be made.
• Gelsectan: a medical device that can improve diarrhea, and contains xylo-oligosaccharides, xyloglycans and pea protein. The Spanish and Italian national IBS guidelines mention xyloglycan and xylo-oligosaccharides as a first line therapy for IBS-D. To my knowledge this is not available in the US at the time of reviewing.

Damage

• Gluten: under debate. Increases permeability in people with celiac disease. Certainly not everyone will be affected by gluten, but some evidence exists also in people with IBS-D that are positive for human leukocyte antigen (HLA)-DQ2/8.
• Fat: a high fat diet can lead to changes in the microbiome, which reduces the amount of SCFAs and increased barrier dysfunction. So far there is no clear data on whether the type of fat makes a difference.
• Fructose: high amounts cause inflammation in the body and may cause intestinal barrier dysfunction and increased endotoxins in the blood. Has to do with high fructose corn syrup and related foods, not fruit.
• Glucose: this relates to high blood glucose, not sugar in food, so people with diabetes have another good reason to keep their blood sugar in range
• Ethanol: damages gut cells and tight junction proteins, especially in chronic alcohol abuse
• Stress: increases gut permeability and reduces beneficial gut microbial species. The suggested mechanism includes reduced secretion of gastric acid, slower gastric motility, slower small intestinal motility, and a reduced number of antibodies that are meant to protect the gut lining.
• Emulsifiers: polysorbate 80 and carboxymethylcellulose increased permeability and changed the gut microbiota in mice.
• Bile acids: Likely a problem of the microbiota, as gut microbes are responsible for processing bile acids that end up in the colon.