Probiotics are the live microorganisms that, when administered in adequate amounts, confer the health benefit on the host — they are the beneficial bacteria and yeasts that colonise the gut and that are essential for the gut barrier integrity, for the immune tolerance (the ability of the immune system to distinguish between the harmless dietary antigens and the pathogenic microorganisms), and for the metabolic health (including the synthesis of the short-chain fatty acids, the vitamins, and the secondary bile acids). The gut microbiota is the community of the microorganisms that inhabit the gastrointestinal tract — it consists of approximately 100 trillion cells (10 times the number of the human cells in the body) and approximately 1000 species of bacteria, archaea, fungi, and viruses, with the bacterial species dominating. The gut microbiota is now recognised as a separate metabolic organ — it digests the dietary fibre, it produces the vitamins (vitamin K, vitamin B12, folate, biotin), it metabolises the bile acids, it competes with the pathogenic bacteria for the nutrients and the colonisation sites, and it modulates the immune system and the brain function through the gut-brain axis. The dysbiosis (the loss of the microbial diversity and the shift in the microbial composition) is associated with the gut barrier dysfunction, the leaky gut, the systemic inflammation, and the increased risk of the inflammatory bowel disease, the metabolic syndrome, the obesity, the type 2 diabetes, the cardiovascular disease, and the neuropsychiatric disorders — making the probiotic deficiency one of the most important and most modifiable risk factors for the chronic diseases of the modern world.
Probiotics and the Gut Barrier
The gut barrier is the physical and immunological barrier that separates the gut lumen from the internal environment of the body — it consists of the mucus layer, the intestinal epithelial cells (enterocytes and goblet cells), the tight junctions between the epithelial cells, and the gut-associated lymphoid tissue (GALT). The gut barrier prevents the translocation of the luminal contents (bacteria, toxins, undigested food antigens) into the bloodstream, and it is therefore essential for the prevention of the systemic inflammation and of the autoimmune diseases. The probiotics maintain the gut barrier integrity through multiple mechanisms — they produce the short-chain fatty acids (particularly the butyrate) that are the primary energy source for the colonocytes and that promote the mucus production and the tight junction integrity; they compete with the pathogenic bacteria for the colonisation sites and for the nutrients; they produce the antimicrobial peptides (bacteriocins) that inhibit the growth of the pathogenic bacteria; and they modulate the immune system through the activation of the pattern recognition receptors (TLRs and NLRs) on the epithelial cells and the immune cells. Without adequate probiotics and their beneficial effects on the gut barrier, the tight junction integrity is compromised (producing the leaky gut), the bacterial translocation increases, and the systemic inflammation develops — which are the hallmark of the probiotic deficiency and of the dysbiosis.
The clinical importance of the probiotics for the gut barrier integrity is underscored by the observation that the probiotic supplementation reduces the markers of the gut barrier dysfunction and the systemic inflammation in people with the leaky gut and with the inflammatory conditions. A meta-analysis of 30 RCTs in over 1500 participants found that the probiotic supplementation significantly reduced the gut permeability (as measured by the lactulose/mannitol test), reduced the zonulin levels (a marker of the tight junction dysfunction), and reduced the CRP and the IL-6 — demonstrating the potent gut barrier-protective effect of the probiotics.
Practical Application
For general probiotic supplementation for the gut health and for the immune support, the evidence-based approach is to supplement with a multi-strain probiotic that provides at least 10-20 billion CFU daily of the well-characterised probiotic strains — particularly the Lactobacillus and the Bifidobacterium species (such as L. rhamnosus GG, B. lactis BB-12, L. acidophilus NCFM, B. longum BB536). The probiotic should be taken with the meals or with the fibre-rich foods (to provide the prebiotics that support the probiotic survival and colonisation), and it should be stored in the refrigerator (to maintain the viability of the live microorganisms). The duration of the probiotic supplementation is important — the benefits are most consistent with the supplementation for at least 4-8 weeks, and the effects may not persist after the discontinuation of the supplementation. For comprehensive gut and immune support, probiotics pair well with the prebiotics (which are the non-digestible fibres that selectively feed the beneficial bacteria and that enhance the probiotic colonisation — the combination of the probiotics and the prebiotics is called the synbiotic approach and is more effective than either alone), with the glutamine (which is the primary energy source for the intestinal epithelial cells and which supports the gut barrier integrity), with the zinc (which is required for the tight junction integrity and for the immune function), and with the vitamin D (which has immunomodulatory effects and which works synergistically with the probiotics for the immune tolerance).
Leave a Reply