Probiotics – the Vitamins of the 21st Century

Introduction to the gut microbiome and probiotics 
The microbes that inhabit our gut have co-evolved with us and our ancestral species for more than 539 million years. We have about 1000 different bacterial species in our gut, and the total number is about 100 trillion bacteria. The total number of bacteria in our gut is nearly three times the number of cells in the human body. As a matter of fact, we rely on our microbiome for functions that are not encoded by the human genome (human DNA)! Which is why many bacteria in our gut are beneficial for our health. In fact, in a healthy gut, ninety percent of the bacteria are good bacteria. The relationship between our gut bacteria and us is thus mutualistic – they benefit us, and we benefit them. Our gut microbiome diversity decreases as we age and is also decreased in people with obesity or Irritable Bowel Syndrome.
Our human ancestors often ate fermented foods, such as kefir, yogurt, kimchi and sauerkraut, which contain good bacteria. In fact, Elie Metchnikoff (a Russian zoologist who won a Nobel Prize in 1906 and first discovered the fact that there are beneficial bacteria in our gut) theorised that Bulgarian peasants who drank yogurt with Lactobacilli lived longer than people elsewhere because of the bacteria they ingested with the yogurt. The World Health Organization defines probiotics as “live micro-organisms, which, when administered in adequate amounts, confer a health benefit on the host.” The beneficial bacteria that inhabit the human gut are our endogenous probiotics. 
The benefits of probiotics 
Note that good bacteria inhibit the growth of bad bacteria by taking up the space (the surface of cells lining the gut) that would otherwise be taken up by harmful bacteria and by eating the nutrients bad bacteria would otherwise use. Good bacteria make compounds (metabolites), known as postbiotics, that combat bad bacteria. Good gut bacteria assist us in absorbing nutrients such as calcium. They even make digestive enzymes and synthesise many vitamins. Beneficial bacteria maintain the cell layer lining the gut and make fatty acids from sugars that we cannot digest on our own. These fatty acids are used as nutrients by the cells lining the gut. In addition, good bacteria help the gut make more mucin, a slimy substance that protects the gastrointestinal tract from friction and from bad bacteria. Furthermore, good bacteria assist in protecting the body from toxins. 
Our microbiome is important for our development. Children born naturally have a better microbiome, which gives them better health, than children born via Caesarean section. Also, children get good bacteria from their mother’s milk, and it is better than formula. Having the right microbiome early on is essential for development, including staving off diseases such as asthma and perhaps autism spectrum disorder. Emerging evidence suggests that probiotics often help with Irritable Bowel Syndrome, Inflammatory Bowel Diseases, lactose intolerance, obesity, inflammation, Type 2 diabetes, Leaky Gut Syndrome, aging, cardiovascular problems, colon cancer, tooth decay, gum disease, UTIs, prevention of allergies, neurodegenerative and psychiatric disorders and reduction of inflammation in autoimmune disorders. 
Prebiotics and their benefits 
Prebiotics are the nourishment that our good gut bacteria feed on. Prebiotics (such as inulin and resistant starches) are fibers that cannot be digested by our own digestive system and are not broken down by stomach acid. They thus pass through the stomach undigested until they reach the small intestine and large intestine, where they are digested and fermented by our gut bacteria, which use them as food. Prebiotics are important because the right prebiotics can enable good pre-existing bacteria in your gut to replicate and grow in number. They are also important because our gut bacteria make short-chain fatty acids (SCFAs, such as butyrate) from fermented prebiotics. The SCFAs are beneficial: they maintain the gut lining, help with water absorption and “modulate immune function”. Butyrate helps prevent colon cancer. 
Are probiotics safe and effective? 
Some bacteria in probiotics might not be safe for individuals who have a weakened immune system, as they might get infections. In general, probiotics are considered as safe for people who are healthy. As with any supplement, talk to your doctor before taking probiotics. Probiotics must be used within the expiration date. In addition, people with severe health conditions must be closely monitored when taking probiotics. Probiotic bacteria that have not been properly researched and clinically proven to be safe could transfer antibiotic resistance genes to your gut bacteria or could make toxic substances. Also, probiotics that were not bought from a reliable manufacturer might include harmful bacteria, which are not supposed to be in the probiotic. 

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