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Gut Health

Probiotics explained: benefits, foods and how they work

21/08/20256 min read

Female holding a bowl of yoghurt in green bowl

You’ve heard plenty about ‘good’ bacteria, but what do probiotics actually do? Our expert breaks down how they work, their potential benefits and where to find them

Summary

1What are probiotics?

Probiotics contain certain strains of ‘good’ bacteria and yeasts. They can be taken as daily supplements or enjoyed in foods.

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2How do probiotics work?

Probiotics are thought to work by encouraging the growth of ‘good’ bacteria in our bodies, which help stop ‘bad’ bacteria from growing.

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3What are probiotics good for?

Probiotics may help restore gut balance after it’s been disrupted by things like illness or infection.

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What are probiotics?
Types of probiotics
How do probiotics work?
What are probiotics good for?
Probiotic foods: natural sources of probiotics

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Gut Health

Bacteria often get a bad rap but they’re actually important for keeping your body healthy.¹ In fact, your body hosts between 500–1000 different species of bacteria at any one time (not to mention the viruses and fungi tagging along).¹It might sound scary but this collection of ‘good’ bacteria, viruses and fungi is known as your microbiome – and it’s actually a good thing.^1,2

Found in places like your skin, gut and mouth, your microbiome assists your immune system, supports your gut health and helps keep everything running smoothly.^1,2 But if the balance of microbes gets disrupted, it can lead to a whole host of problems.² That’s where probiotics may help. Packed with beneficial strains of bacteria and yeasts, they may potentially support your gut microbiome and overall health.³

To unpack this further, we asked consultant gastroenterologist Professor Laurence Lovat for his expert thoughts on what probiotics really do, how they work, if they have any benefits and whether they live up to the hype.

What are probiotics?

Probiotics are certain strains of ‘good’ bacteria and yeasts.⁴ They can be taken as daily supplements or enjoyed in foods like yoghurt.⁴Probiotics are thought to offer various potential benefits, such as helping restore gut balance after illness or infection and supporting digestive comfort, although evidence for many health claims remains limited.⁴

Since they’re classed as food supplements, probiotics don’t have to undergo the same strict testing as medication.⁴ This means that we don’t always know how effective a particular product really is, if it contains the specific bacteria strain it claims or if those bacteria will even make it to the right part of the body.⁴With so many different probiotics available, each containing a variety of microorganisms, they can have unique effects on the body.⁴ Let’s take a closer look at some of the most common ones.

Types of probiotics

Probiotics are identified by the name of the specific bacteria or yeast strain they contain.⁵Some of the most common species include:⁵

Chilled Greek Yogurt with Honey and almonds

Lactobacillus
Bifidobacterium
Saccharomyces
Streptococcus
Enterococcus
Escherichia
Bacillus

Only specific strains of bacteria that have demonstrated potential health benefits are recognised as probiotics.⁵So, how do these ‘good’ strains of bacteria and fungi help keep your body healthy?

How do probiotics work?

Probiotics are thought to work by encouraging the growth of ‘good’ bacteria in our bodies, which in turn help stop ‘bad’ bacteria from growing and causing diseases.^3,6Think of your body like a car park: when spaces are filled with ‘good’ bacteria, there’s no room for the harmful ‘bad’ bacteria to park and cause trouble.

Certain specific probiotic strains have been studied for their potential to support the immune system, though findings differ and the exact ways they may work aren't yet fully understood. Other strains of probiotics may also have properties that make them useful for specific areas of health, especially when it comes to gut health and digestive health.^3,5,7,8

What are probiotics good for?

Before we get into the potential benefits of probiotics, it’s important to realise that not all health claims surrounding them are backed up with strong, high-quality evidence.^4,9 The results also vary depending on the type of probiotic.^4,9So, you may be left wondering: should I take probiotics? That’s totally up to you. The NHS advises that probiotics are generally safe for most people with healthy immune systems but if you have any underlying health conditions (especially ones that affect your immune system), it’s a good idea to check with your doctor first.⁴

If you decide to give probiotics a try, how long will they take to work? That really depends on the type of probiotic you’re taking, its strength and what you’re hoping to achieve.^3,5-10If you’re focusing on supporting your digestion, the NHS and BDA (British Dietetic Association) suggest trying a probiotic for at least four weeks to see if it works for you.^11,12 If they don’t work, try another type or stop taking them – they won’t work for everybody.¹²

Probiotic supplements are one way to go. They can contain a single strain or a blend of several different types, so it’s worth doing a bit of research to find the best option for your needs.^3,8Alternatively, you can support your gut health naturally with probiotic-rich foods.^3,5

Probiotic foods: natural sources of probiotics

Fermented foods are a great natural source of probiotics.^3,5 Stick to foods that haven’t been processed after fermentation to get the highest concentration of live cultures.⁵Yoghurt is a popular choice for probiotics but there are plenty of other fermented foods that may contain probiotics, including:^5,13

some cheeses
kimchi or sauerkraut (fermented cabbage)
kombucha (fermented tea)
miso (fermented soybean-based paste)
some pickles
raw, unfiltered apple cider vinegar
kefir
tempeh

Probiotics FAQs

What do probiotics do for your body?

Probiotics are certain strains of ‘good’ bacteria and yeasts that may help support the balance of microorganisms in your body.⁴ Different strains work in different ways, with research exploring their potential roles in areas including digestive, gut and immune health.^3,5,7 However, the evidence varies depending on the specific strain and benefit being studied.^4,9

What foods naturally contain probiotics?

Fermented foods are some of the most well-known natural sources of probiotics.^3,5 These include yoghurt, kefir, kimchi, sauerkraut, miso, tempeh and some cheeses and pickles.^5,13 However, not every fermented food contains live probiotics, as processing and preparation can affect whether the microorganisms survive.⁵ In a rush? Why not blitz up a kefir and fruit smoothie for a quick, easy breakfast.

How long do probiotics take to work?

There’s no set timeframe, as it depends on the probiotic strain, its strength and what you’re taking it for.^3,5-10 If you’re trying a probiotic for digestive symptoms, the NHS and British Dietetic Association recommend taking it for at least four weeks to see whether you notice a difference.^11,12 If it doesn’t help, you could try a different type or stop taking it.

What's the difference between probiotics and prebiotics?

Think of them as two different parts of the gut-health picture. Probiotics are live microorganisms that can support your health when you get enough of them, while prebiotics act as food for certain ‘good’ microorganisms already living in your body, helping them to grow and thrive.¹⁴ So, the key difference is that probiotics are the microorganisms themselves, whereas prebiotics provide something for certain microorganisms already living in your body to use.

The final say

While more research is still needed, some specific strains in probiotics have been found to have a potential benefit in gut health and immune response.^3-5,10They’re generally safe for most healthy people but it’s always a good idea to do your own research before trying any supplement and speak to your GP for advice if you have any underlying health conditions.³

We’ve talked about probiotics but what are postbiotics and what about prebiotics?

Disclaimer – This article provides informational advice and is not a substitute for medical care. Working with experts for accuracy, we take great care to ensure the information is up-to-date and relevant. However, you should always consult your GP or healthcare professional before using supplements or alternative products, particularly if you have medical conditions or are under supervision.

Sources

1. Gilbert JA, et al. Current understanding of the human microbiome. Nature Medicine. 2020;24(4):392–400. https://pmc.ncbi.nlm.nih.gov/articles/PMC7043356/

2. Hou K, et al. Microbiota in health and diseases. Signal Transduct Target Ther. 2022;7(1):135. https://doi.org/10.1038/s41392-022-00974-4

3. Bodke H, Jogdand S. Role of probiotics in human health. Cureus. 2022;14(11):e31313. https://doi.org/10.7759/cureus.31313

4. NHS. Probiotics [Internet]. [cited 2025 Feb 25]. Available from: https://www.nhs.uk/conditions/probiotics/

5. NIH. Office of Dietary Supplements - Probiotics [Internet]. [cited 2025 Feb 25]. Available from: https://ods.od.nih.gov/factsheets/Probiotics-HealthProfessional

6. Mazziotta C, et al. Probiotics mechanism of action on immune cells and beneficial effects on human health. Cells. 2023;12(1):184. https://doi.org/10.3390/cells12010184

7. Varela-Trinidad GU, et al. Probiotics: Protecting our health from the gut. Microorganisms. 2022;10(7):1428. https://doi.org/10.3390/microorganisms10071428

8. Cunningham M, et al. Applying probiotics and prebiotics in new delivery formats – is the clinical evidence transferable? Trends Food Sci Technol. 2021;112:495–506. https://doi.org/10.1016/j.tifs.2021.04.009

9. Brüssow H. Probiotics and prebiotics in clinical tests: An update. F1000Res. 2019;8:1157. https://doi.org/10.12688/f1000research.19043.1

10. Kristensen NB, et al. Alterations in fecal microbiota composition by probiotic supplementation in healthy adults: a systematic review of randomized controlled trials. Genome Medicine. 2016;8(1):52. https://doi.org/10.1186/s13073-016-0300-5

11. NHS. Good foods to help your digestion [Internet]. [cited 2025 Feb 25]. Available from: https://www.nhs.uk/live-well/eat-well/digestive-health/good-foods-to-help-your-digestion

12. British Dietetic Association. Probiotics and gut health [Internet]. [cited 2025 Apr 3]. Available from: https://www.bda.uk.com/resource/probiotics.html

13. Azizi NF, et al. Kefir and its biological activities. Foods. 2021;10(6):1210. https://doi.org/10.3390/foods10061210

14 Gibson GR, Hutkins R, Sanders ME, et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nat Rev Gastroenterol Hepatol. 2017;14(8):491–502. Available from: https://doi.org/10.1038/nrgastro.2017.75