Episode 90: What are probiotics?

Summary by Ellie Roberts


This episode is sponsored by Symprove.


On this week’s episode, Dr Bahijja Raimi-Abraham discusses probiotics with Professor Simon Gaisford, Chair in Pharmaceutics at University College London School of Pharmacy.





Probiotics and prebiotics, symbiotics and synbiotics…?

“A living (bacterial) organism which, when swallowed in sufficient quantity, provides a health benefit to the host” – definition of a probiotic by the World Health Organisation (WHO)

Probiotics are usually taken with the intention of improving health, however this is only possible if the probiotics are able to survive and grow in the body’s internal environment. This is where prebiotics come in – basically food for probiotics!

Symbiotic organisms live in harmony with one another in a way that is mutually beneficial – for example, the probiotic bacteria in your gut have a symbiotic relationship with you.

The term synbiotic on the other hand is used to describe a combination of probiotics and prebiotics: both the bacteria and the food stuffs together.


Your body is the home of many bacteria

“90% of the cells in your body are bacterial” – Professor Simon Gaisford

If you look at your body as a whole, there are likely going to be a lot of bacteria living all over you, most of them residing in the gut. Although, there are also places where they aren’t – such as the insides of your brain…

Generally, the parts of your body which are most exposed to the outside world, such as your nose and mouth, are funfairs for bacteria. The mouth forms the beginning of the gastrointestinal (GI) tract, and as you travel further down, the number of bacteria greatly increases. When looking at the stomach, there aren’t really that many bacteria because it is such a hostile environment due to the acid – part of its function is to keep bacteria out of the stomach.

However, as you start to enter the colon, there are trillions and trillions of bacteria.


What is the purpose of probiotic supplements?

As there already exists an army of probiotics within your colon, probiotic supplements simply add a few more to the total population. The bacteria within your colon aren’t all good – there are also bad bacteria which live inside your gut. What’s important is the balance between these two populations – if the bad bacteria start to overpower the good, negative symptoms arise and this could potentially lead to a range of diseases. Stress, antibiotics, smoking, alcohol, lack of exercise and poor diet can all tilt the balance in favour of the bad bacteria. Along with a healthy lifestyle, probiotic supplements help keep the good bacteria on top.



Should you take probiotic supplements?

If you looked at one person’s gut, you would see a huge diversity of bacterial species – anywhere between 6 to 10,000 different species! However, many of those species will be very low in number, and generally there are a few species which tend to dominate. A lot of probiotic supplements which are sold contain members of these dominating species, so if you were to take them, your gut flora wouldn’t fundamentally change and there wouldn’t be much noticeable difference. Therefore, taking probiotic supplements which contain a range of species to increase diversity would be more beneficial to your health.

As everyone’s balance of gut bacteria and state of their internal environment greatly differs, the type of probiotic supplement which would benefit you the most will be unique to you. However, by trying different probiotic supplements you can find out what works for you and what you could have been lacking in originally.


How do probiotics actually work?

Probiotics are generally grouped under “lactic acid bacteria” (Lactobacillus), meaning they produce lactic acid. Like all living creatures, bacteria consume food stuffs that they find in their surrounding environment and produce waste (lactic acid in this case).

Lactic acid is a very weak acid, so the gut can tolerate quite a lot of it. Lactic acid creates an environment which has a lower pH. Native “good” bacteria are good at surviving in such conditions, however infectious bacteria which are not native to the gut, such as E. coli, can’t easily survive in acidic conditions. Therefore, having lots of good gut bacteria and taking beneficial probiotics can increase the amount of lactic acid produced, lowering the pH of the colon. As the amount of lactic acid rises, it also forms a food stuff for the good bacteria, allowing them to grow and multiply, and produce short chain fatty acids, which are hugely implicated in good gut health.


So, if you have a gut infection, taking probiotics can be greatly beneficial, through both destroying bad bacteria and encouraging the growth of good bacteria.


Want to know more?

Check out these links:

The role of gut microbiota in nutrition and health - https://www.bmj.com/content/361/bmj.k2179

How antibiotics alter the gut microbiome and health - https://www.nature.com/articles/d42859-019-00019-x

The impact of the gut microbiome on mental health - https://asm.org/Articles/2020/February/Of-Microbes-and-Mental-Health-Eating-for-Mental-We



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