What are probiotics and what do they do?

Discover the benefits of probiotics and prebiotics, the best foods, drinks and supplements, and how to boost good gut bacteria for a healthy digestive system.

What are probiotics and what do they do?

The intestinal tract is the organ in the body that digests and absorbs food. It is populated by trillions of bacteria that are required for keeping the body healthy. These bacteria can be affected by a number of aspects including antibiotic use, some medications and infective diarrhoea. When this occurs, probiotics can help to reset the balance.

What are probiotics and how do they work?

Probiotics are living organisms that are found naturally in foods such as yogurt, kimchi, sauerkraut, miso and kefir. They are known as ‘good’ or ‘friendly’ bacteria as they compete for space and food against harmful bacteria and prevent them from settling in the gut. 

What are prebiotics and how do they work?

Prebiotics are specific non-digestible carbohydrates that act as food for probiotics in the gut. They occur naturally in the diet and are found in foods such as garlic, bananas, oats, onions and leeks. These foods aren’t eaten in large quantities in the UK but can be added into food products such as fructo-oligosaccharides. As the research into prebiotics is in the very early stages, the absence of robust evidence prevents the widespread use of prebiotics for clinical conditions. However, foods containing prebiotics are also the components of a healthy diet and should therefore be consumed regularly.

What can negatively affect gut bacteria?

There are a number of components that negatively affect gut bacteria including antibiotics, fermentable carbohydrates and smoking.
Designed to fight infections, antibiotics reduce and deplete the natural bacteria living in the gut. Resistance to antibiotics is becoming a serious problem worldwide and it is for this reason that we should only take these when absolutely necessary. 

A long-term reduced intake of fermentable carbohydrates for the treatment of IBS (as in a low FODMAP diet) can also negatively affect the bacteria in the gut. It is therefore important that these foods are only omitted for a specified time under the guidance of a specialist dietitian as the implications of long term avoidance needs further research. 
Smoking also has a negative impact on the bacterial composition of the gut in addition to the well documented health risks it carries.

What are the different types of probiotics?

There are numerous types of probiotics and each has different characteristics. They may be combined with others or appear on their own in powder, tablet or liquid dietary supplements. At the moment, foods that naturally contain probiotics are not eaten regularly in the UK and supplements are becoming more popular. The most common probiotics include lactobacillus acidophilus and bifidobacterium. These differ as they are made up of different types or strains of bacteria and are recommended for different clinical conditions. Lactobacillus acidophilus have been clinically shown to lower the incidence of antibiotic associated diarrhoea and can also result in a shorter length of stay in hospital for some. In order to experience this benefit, a vast quantity of food containing probiotics would need to be consumed. It is therefore easier and more effective to take a recommended probiotic supplement. 
For those with a diagnosis of IBS, supplements containing bifidobacterium have been shown to reduce symptoms, including bloating, cramping and stool frequency, and can be taken for up to eight weeks.

What are the health benefits of probiotics?

Probiotics have been shown to improve symptoms in IBS, traveller’s diarrhoea and the duration of antibiotic associated diarrhoea. There is emerging evidence that probiotics may improve cholesterol levels in people with type II diabetes and could play a role in benefitting cold or flu outcomes during stressful periods. However, these are very small studies and more research is needed before robust recommendations can be made. 

What are the risks of probiotics?

Generally, probiotics are safe for healthy individuals, however those with a compromised immune system may be at risk and should seek advice from a specialist dietitian or GP before starting.

What should we look for when choosing a probiotic supplement?

There are two key issues when choosing a probiotic: the first is to ensure that the product contains enough bacteria to have an effect (107 to 1010 probiotic cells per gram); the second is to ensure that it survives the acidic environment of the stomach in order to reach the large intestine. Examples of probiotics that meet this criteria include Alforex, Yakult, Symprove and VSL #3.  Each of these is designed to treat different symptoms, so if you are thinking about taking a probiotic, seek advice from a specialist dietitian or GP to ensure you take the correct one. 
Unless stated differently by manufactures, probiotics should be taken for a minimum of four weeks before effects may be seen. If no improvement is noted, it is recommended that you try another brand or stop completely.

Is it best to take probiotics and prebiotics as foods, supplements or drinks?

If you are thinking about taking a probiotic or prebiotic and are unsure where to start or what to take, ask for help from a specialist. There are so many in the market it can be difficult to make a decision on what to choose. The evidence is very much linked to the supplement so whether it’s a powder, tablet or drink you’re looking for, choosing the right one should depend on the symptoms you’re experiencing.  


What is a low FODMAP diet?
The health benefits of fermenting
What to eat for better digestion
The health benefits of miso

This article was published on 24 March 2017.

Emer Delaney BSc (Hons), RD has an honours degree in Human Nutrition and Dietetics from the University of Ulster. She has worked as a dietitian in some of London's top teaching hospitals and is currently based in Chelsea.

All health content on bbcgoodfood.com is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. If you have any concerns about your general health, you should contact your local health care provider. See our website terms and conditions for more information.

Have you tried probiotics or prebiotics, or do you have any questions about them? Ask us in the comments below.

Comments, questions and tips

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2nd Apr, 2017
We have used probiotics and prebiotic on horses since 1986, notice many benefits such less colic, healthier foals, better hoofs, helps with stomach ulcers, as well as cost savings. A hard keeping horse generally does not absorb the nutrients well the probiotics clearly improved that. Also dogs can benefit as well as any other animal not living in its natural environment. Our dogs have very little gas and no doggy smell. 16 years ago I found a blend that has worked for me since then I have not lost a day to colds, flu my issue of gas, bloat greatly reduced, my craving for sweets greatly reduced
2nd Apr, 2017
Has over use of farmland and processed food reduced the natural availability of beneficial bacteria
2nd Apr, 2017
Why do you produce no evidence? e,g, NHS reports, such as this: www.nhs.uk/news/.../No-evidence-probiotics-are-beneficial-for-healthy-adults.aspx - "Essentially, none of the studies provided evidence that probiotics had a beneficial effect on gut bacteria ..." Is this knowledgeable reporting, or is it advertising for useless products?
goodfoodteam's picture
13th Apr, 2017
Thank you for your query. We asked dietitian Emer Delaney to respond to your questions and this is what she said, "My article lists a number of different evidence-based articles which I've listed below: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2658588/, http://www.ibs-care.org/pdfs/ref_150.pdf, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3278944/, https://www.ncbi.nlm.nih.gov/pubmed/23548007, https://www.ncbi.nlm.nih.gov/pubmed/17298915 and https://www.ncbi.nlm.nih.gov/pubmed/24772726. The study I believe you're referring to was looking at the use of probiotics in healthy people. My article and the supporting evidence includes people with specific medical conditions such as IBS, people who are in hospital and those suffering from diarrhoea from antibiotics i.e. not the healthy population. In addition, the article states the trials were still highly variable in their methods and design - the type of probiotics given and how gut bacteria were assessed were different, therefore affecting the quality of the data. The studies also contained many quality limitations as the participants were not blinded which can significantly affect results. Only one study looked at the number needed to treat, which again can result in poor outcomes and statistical assessment was lacking in many of the studies. Finally, none of the trials were from the UK, so the formulations used may differ from those on the UK market. All of the above results in a very weak conclusion." We hope this helps to allay your concerns.
reneemeryl's picture
25th Apr, 2018
I have been taking probiotics for several years now. When I first started taking them, I had been getting increasing attacks of gout, but I didn't take them for that reason. Soon, I realised that I had stopped getting gout, except for the very occasional attack if I had been taking antibiotics, so it wasn't all in the mind, because I hadn't expected the attacks to stop. I get mine from the well-known health shop and they need refrigerating after opening.
2nd Apr, 2017
The better products are refridgerated and the numbe s are in the billions, much more than your average yogurts.