How do probiotics work?

Kathy Wheddon Nutritional Therapist DipION

Probiotics are good bacteria or yeasts. But exactly how do they work? Let’s take a look at the journey that a probiotic goes on from the moment we swallow it, until the moment that it reaches its destination and starts to do its important work.

Woman holding her tummy

Surviving stomach acidity:

Probiotics are best taken in the morning with, or just after, breakfast. The reason for this is that the acid in our stomach is at its weakest in the morning, and this acidity is buffered still further by the presence of food in the stomach. Probiotics are living things (either bacteria or yeasts), and because of this they can be damaged by excessively acidic conditions, so timing can be a key factor to ensure their survival through the harsh stomach environment. By taking our range in the morning with breakfast you can ensure that the bacteria travel safely through the acidic stomach environment and arrive at their destination in the intestines. To learn more, read the article: Do probiotics survive to reach the gut alive?

That being said, we only select very robust strains of bacteria for our products, and these are naturally resilient to all but the very strongest of acid conditions. We test all the strains we use at different acid levels to ensure their viability, and it is the strains themselves which are tested rather than the encapsulated product, which means that our bacteria can safely be taken out of their capsules for those individuals who struggle to swallow pills. Find out more by reading the article: Are all types (strains) of friendly bacteria the same?

microscope bacteria

Adherence to the gut wall:

Once through the stomach the probiotics are released in to the small intestines, where some strains of probiotic will take up ‘residence’ for a short time, and adhere (or attach to) the lining of the gut wall. Other strains may not adhere to the gut lining until much further down in the digestive tract, and may not take up residence until they reach the large intestine (or bowel).

Where probiotics choose to reside is governed predominantly by the specific conditions in different areas of the gut, and the type of bacteria in the microbiome. Bacteria are either classed as 'anaerobic' or 'aerobic': an anaerobic organism does not require oxygen to live whereas an aerobic organism needs an oxygenated environment.Some bacteria are known as 'facultative anaerobes' which means that they can adapt to an area with or without oxygen.

Some areas of the gut have more oxygen available, whereas other areas have little or no oxygen, making those areas only suitable to anaerobic strains of bacteria. Additionally the pH (levels of acidity or alkalinity) differ at different points along the digestive tract, with the small intestine typically being more acidic than the large intestine. Although, as we have learned, it can be a challenge for probiotic bacteria to travel through the highly acidic stomach, which can reach acidity levels of around pH 1.5, probiotic bacteria actually prefer a slightly acidic or pH neutral environment. All of these factors influence where a specific bacteria chooses to ‘live’.

In order to start to multiply a probiotic needs to have attached to the lining of the intestine (at whichever point along its length). It is only once they have attached/adhered that they can replicate and grow in numbers, and it is then that they can start to exert their beneficial effects on our health. For this reason, we perform in vitro trials (trials that are performed in a laboratory) on all of our strains of bacteria to check that they are able to adhere to gut epithelial cells.

Diagram of a gut wall/ Probiotics Learning Lab

Pathogen inhibition:

By rapidly growing in numbers, probiotics are able to ‘crowd out’ any pathogenic (or ‘bad’) strains of bacteria that may have been able to take hold. In effect the probiotic strains compete with pathogens for both their food sources and their space in which to live, making their existence much harder.

Probiotics also produce certain acids which make the gut environment less hospitable for pathogens to flourish in, whilst optimising the environment for their own benefit. In general pathogenic species of bacteria prefer a more alkaline environment, so by altering (in this case, lowering) the pH of the intestines probiotics can limit their growth.

Once any pathogenic overgrowth has been reduced, a person should typically start to feel an improvement in health symptoms, due to the fact that pathogens produce many toxins and other substances that negatively affect our health. While pathogens produce toxins, probiotic strains of bacteria produce beneficial substances such as certain vitamins and short-chain-fatty-acids that have a positive impact on our overall health.

Our intestines house a delicate ecosystem of microbes, and many factors effect which strains flourish, and which ones may struggle. Taking a probiotic supplement that is known to survive stomach acids, and then also known to have good adherence capabilities to the gut wall lining, not only ensures that the supplemented strains of gut bacteria can temporarily colonise, but also that the gut environment is altered in such a way that our own natural resident strains of ‘friendly’ bacteria can recover and replenish.

To learn more, read the following articles:

When should I NOT take probiotics?

The microbiome - all you need to know

This FAQ has been answered by Kathy Wheddon, Nutritional Therapist DipION.