What is ‘leaky gut’?

‘Leaky gut’ is known as reduced intestinal barrier function in the gut research world and is a symptom of many conditions rather than a condition in its own right. The symptoms vary depending on the condition it is associated with, so if you are reading something that says “the symptoms of leaky gut are X, Y and Z” then it is most likely inaccurate. That said, there are feasible mechanisms by which intestinal permeability could influence gut symptoms or ‘extra-intestinal’ symptoms like fatigue, lethargy and ‘brain fog’.

Types of ‘leaks’

To better understand the science of the intestinal barrier and how it may leak, it is important to know that the barrier varies in thickness along the intestinal tract. Digestion relies on some degree of permeability (or no nutrients would be absorbed) and that there are two main types of leaks.

1. The ‘leak’ pathway is regulated by tight junctions and only allows very small molecules to pass.

2. The ‘unrestricted’ pathway (like with an intestinal ulcer) does not rely on tight junctions, which means potentially harmful antigens can pass from the gut into the bloodstream and body systems.

The focus of most ‘leaky gut’ research is the small intestine, where the barrier is thinner than in the colon, and where most nutrient absorption occurs. Recent research has investigated the extent to which a protein called zonulin is involved in leaky gut (1). Zonulin influences the size of the gaps between intestinal cells, so it controls how nutrients, water and cells move in and out of the gut. It is hypothesised that when (too much) zonulin is present, the normally tight junctions between the intestinal cells ‘leak’ and eventually damage the intestinal wall. Elevated levels of zonulin have been reported in people with coeliac disease or wheat sensitivity compared to people with IBS or no gut problems, but there is not yet consensus about whether gluten directly causes ‘leaky gut’ (2).

Dietary Factors 

Dietary factors most likely to increase intestinal permeability or ‘leaky gut’ are:
  • Long term excess dietary fats, especially saturated (hard) fats because they stimulate bile acids, change the balance of ‘harmful’ vs. ‘helpful’ gut bacteria (dysbiosis) and stimulate inflammatory and other immune responses (3).
  • Emulsifiers can damage the intestinal barrier, decrease microbial diversity and induce mucosal inflammation. Specifically, CMC (466) and polysorbate 80 (433) cause thinning of the mucus layer, influencing bacteria numbers and movement across the gut barrier and inflammatory responses (2).
  • Alcohol (ethanol) also disrupts intestinal permeability by directly affecting intestinal cells and tight junctions, with as little as 20 grams of alcohol (2 standard drinks) shown to cause increased permeability in a human study (2).
Dietary factors that help maintain intestinal integrity include:
  • ‘Prebiotics’ like soluble fibres (in grains, legumes, some veggies and some supplements) help prevent dysbiosis, build the intestinal mucus layer, support short chain fatty acid production and improve in host immunity. Probiotic foods or supplements may complement these prebiotic foods, but more human studies are needed before it is possible to recommend specific combinations of pre- and probiotics (synbiotics).
  • Polyphenols from fruits and vegetables have been shown (in animal studies) to be helpful in reducing inflammatory responses and enhancing protective gut responses, with different polyphenols (from different coloured fruit and vegetables) having different mechanisms of action, highlighting the needs for variety in fruit and veg in the daily diet.
  • Glutamine is an amino acid that is usually abundant in the diet and human body. People who need extra protein to recover from illness or injury may benefit from extra dietary glutamine to protect intestinal cells against cellular stresses and inflammation. Foods and supplements that are high in glutamine include meats, fish, eggs, nuts, beans, milk and high-protein supplements.
  • Ensuring that levels of vitamin D and zinc in the blood are adequate is also reported to be important in maintaining optimal gut barrier integrity.

Summary

‘Leaky gut’ means increased or impaired intestinal permeability and is a characteristic of several gut disorders, rather than being a gut condition itself.

Advances in measuring changes to intestinal permeability should help researchers to better understand impaired intestinal permeability.

High fat diet, emulsifiers and alcohol damage the intestinal barrier.

Dietary factors that help restore intestinal barrier function include prebiotics, probiotics, amino acids, minerals and avoiding dietary intake of components that damage the barrier.

Most research to date comes from animal studies, so human research showing which dietary components restore or maintain the gut barrier is needed.

 References 

(1) Talley NJ, Holtmann GJ, Jones M, et al. Zonulin in serum as a biomarker fails to identify the IBS, functional dyspepsia and non-coeliac wheat sensitivity. Gut 2020;69:1719–22.

(2) Camilleri, M. Leaky gut: mechanisms, measurement and clinical implications in humans. Gut 2019; 68(8): 1516-1526.

(3) Netto Candido TL, Bressan J, Alfenas RdeCG. Dysbiosis and metabolic endotoxemia induced by high-fat diet. Nutr Hosp 2018;35:1432–40.