Before any probiotic, whether a food or a supplement – can have a benefit to your gut microbiome, it must be able to survive the acidity of your stomach, the temperature and the lack of oxygen in the GI tract, and lastly the availability and competition for chemicals and nutrients required for it to exist and colonise.
Immediately after swallowing, any bacteria will encounter the enzymes in your saliva before being swallowed and reaching the stomach. Once in the stomach the bacteria is then exposed to a strong acid bath with a pH less than 3 – as well as destructive digestive enzymes, such as pepsin, which break down proteins into smaller amino acids. Most bacteria we consume is not able to survive this.
However the bacteria that do survive then move to the small intestine where the acidity decreases, but they are exposed to more digestive enzymes such as amylase, lipase and protease as well as bile. Bacteria must be able to survive this process of digestion and recover in order to colonise and grow either in the small intestine or the colon.
According to Bethlehem University, probiotics contained or consumed in milk and other dairy products have a greater chance of survival as the dairy can reduce the effect of the stomach acid, and increase the chances that the probiotic bacteria will reach the small intestines unharmed.
In a similar way the bacteria contained in probiotic supplements will have a greater chance of surviving your stomach acid if the supplement capsule has an enteric coating – a layer that protects the bacteria from the stomach acid. In this way the probiotic bacteria has a greater chance of reaching the intestinal tract unharmed.
It is thought that only highly resistant bacteria such as the lactobacillus and bifidobacteria genus can survive the stomach acid of the human GI tract. Of these B. animalis, L. casei, L. rhamnosus and L. plantarum have shown the greatest resilience in studies simulating the conditions of the human GI tract.
In all cases the probiotic bacteria are more likely to survive when consumed in sufficient quantities.
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