Leaky gut - what it is and how to improve it

The gut barrier is our greatest physical barrier. It separates us from the outside world, covering a space of 400m² and requiring 40% of our energy. Its mission is to protect us from toxins and micro-organisms while allowing the passage of nutrients through it. Among the cells of our gut are the tight junctions or narrow junctions; these are one of the main mechanisms of regulation of the passage of substances into our interior (1).

Intestinal permeability

The tight junctions are not fixed structures - their environment modulates their function. This modulation of the tight junctions is carried out by the zonulin protein (2). People with a higher expression of zonulin consequently have a more permeable intestine, and when the gut becomes "leaky" and bacteria and toxins enter the bloodstream, it can cause general inflammation and possibly trigger a reaction from the immune system. These people are more susceptible to develop some autoimmune diseases such as type one diabetes, Celiac disease or Crohn's disease. Some symptoms of leaky gut syndrome include bloating, food sensitivities, digestive issues, fatigue, and skin problems (3).

Possible causes

• Gluten. The presence of gliadin (one of the gluten proteins) in the intestine promotes the release of zonulin and increases intestinal permeability (4). People with Celiac disease have a greater response, and for longer, than those without Celiac disease (5).
• Genetics. It is a possible cause although "the genes carry the weapon, the lifestyle pulls the trigger".
• Nutrients or food components. The presence or absence of some nutrients aggravates permeability (6):
  
  • The deprivation of the amino acid glutamine and zinc make the condition worse.
  • Capsaicin, a major constituent of hot peppers, may affect the function and permeability of the intestinal mucosa.
  • The fatty acids EPA and DHA are double-sided, increasing and decreasing the barrier by two different routes.
  • The alcohol. Apart from altering the microbiota and a long list of damages, we add an increase in intestinal permeability.
• Pathogenic bacteria. They cause damage to the structure of the intestinal barrier promoting the development of gastrointestinal disorders (7).
• Stress. It alters bowel movements, microbiota, and permeability (8).
• High-intensity exercise. An excess of it increases intestinal permeability and decreases gut barrier function (9).
• Medicines. Especially non-steroidal anti-inflammatories such as ibuprofen or aspirin (10).

How to improve it

The best way of improvement is to avoid the causes we have seen above, although food is also able to improve the function of our intestinal barrier.

• Nutrients or food components that decrease permeability (11):
  
  • Vitamin D and vitamin A have roles in maintaining the integrity of the intestinal mucosal barrier. The synthesis of vitamin D is done by sun exposure or supplementation if necessary; instead, vitamin A should be eaten - two excellent sources are oily fish and liver.
  • The amino acids glutamine and tryptophan are associated with decreased permeability. Eggs are an excellent option, as they are very rich in both nutrients.
  • B-casein and B-lactoglobulin are two proteins that we can find in cheese or yoghurt.
  • Polyphenols are components of plants with many benefits, including the decrease in intestinal permeability. They include legumes, onions, garlic, berries such as blueberries or raspberries, raw cacao, coffee, or tea.
  • Medium chain fatty acids such as capric and lauric improve the permeability of mucosal tissues in the intestine. These can be found in coconut oil or full-fat yoghurt. 
  • Short chain fatty acids such as butyrate, propionate and acetate. These components are produced after the fermentation by our bacteria of non-digestible carbohydrates. Eating fibre-rich foods, such as fruits, vegetables and legumes, is linked to an increase in short-      chain fatty acids (12).
  • Fatty acids EPA and DHA. We find them in oily fish like salmon or sardines.
• Probiotics. They improve the integrity of the intestine (13). One of the strains most studied and with positive effects is the Lactobacillus plantarum WCSF1 (14).

Our intestine has a preference for some nutrients; a food based on real food is the key to provide the essential nutrients.

References

(1) Intestinal permeability – a new target for disease prevention and therapy
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4253991/)

(2) Zonulin, regulation of tight junctions, and autoimmune diseases
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3384703/)

(3) Alterations in intestinal permeability
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1856434/)

(4) Early effects of gliadin on enterocyte intracellular signalling involved in intestinal barrier function
(https://www.ncbi.nlm.nih.gov/pubmed/12524403/)

(5) Gliadin, zonulin and gut permeability: Effects on celiac and non-celiac intestinal mucosa and intestinal cell lines
(https://www.ncbi.nlm.nih.gov/pubmed/16635908)

(6) Nutritional Keys for Intestinal Barrier Modulation
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4670985/)

(7) The role of epithelial malfunction in the pathogenesis of enteropathogenic E. coli-induced diarrhoea
(https://www.ncbi.nlm.nih.gov/pubmed/19620958/)

(8) Stress and the gut: pathophysiology, clinical consequences, diagnostic approach and treatment options
(https://www.ncbi.nlm.nih.gov/pubmed/22314561)

(9) Exercise, intestinal barrier dysfunction and probiotic supplementation
(https://www.ncbi.nlm.nih.gov/pubmed/23075554)

(10) Intestinal permeability in the pathogenesis of NSAID-induced enteropathy
(https://www.ncbi.nlm.nih.gov/pubmed/19148789)

(11) Nutritional Keys for Intestinal Barrier Modulation
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4670985/)

(12) Fiber and Prebiotics: Mechanisms and Health Benefits
(http://www.mdpi.com/2072-6643/5/4/1417/htm)

(13) Protection and Restitution of Gut Barrier by Probiotics: Nutritional and Clinical Implications
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3864899/)

(14) Effect of Lactobacilli on Paracellular Permeability in the Gut
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3257727/)