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Probiotics and prebiotics

Probiotics are microscopic, live organisms (microbes) that, if you swallow in large enough amounts, are good for your gut health.

Prebiotics are foods that help to increase the numbers and activity of healthy microbes in your gut.

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What is a probiotic?

There are trillions of microscopic organisms in your gut (digestive system), especially the last part of the gut, the large intestine (colon). They are important for your health. They are sometimes called 'healthy', 'good' or 'friendly' bacteria. They rely on what we eat and drink to grow and to increase in number.

Probiotics are medicines, food that has been fermented or food supplements that contain these bacteria. The best known are called lactic acid bacteria (LAB) and bifidobacteria. However, there are others, including a yeast and other bacteria. They are being added to some foods, such as yoghurts, and are also available as capsules, tablets and sachets, and even sprays.

Probiotics are live cultures of bacteria but are not usually harmful. They aren't killed by being stored (as long as they are stored properly) and they can survive the journey through the stomach without being killed by stomach acid.

LABs are used for preserving food by fermenting it, such as in yoghurt, kefir, sauerkraut and kimchi.

What is a prebiotic?

Prebiotics are foods that your body can't breakdown and absorb (digest). They encourage the growth and activity of healthy gut microbes. By doing this they may improve your health.

Common prebiotics:

  • Oligofructose and inulin: found in foods such as wheat, onions, asparagus, bananas, garlic and leeks. Extracted industrially, mainly from chicory root, or manufactured from sucrose.

  • Galacto-oligosaccharides: produced commercially from lactose, a by-product of the dairy industry.

  • Lactulose: a medicine used in the treatment of constipation and severe liver disease. Also produced from lactose.

  • Breast milk oligosaccharides: may be one of the factors that protects breastfed infants from gut infections that cause diarrhoea.

Most prebiotics are food ingredients found, for example, in biscuits, cereals and dairy products. They are used to improve the mouth-feel and acceptability of low-fat foods and to sweeten low-calorie foods.

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What is a synbiotic?

Synbiotic is the word for a product that contains both a probiotic and a prebiotic.

How do probiotics and prebiotics improve your health?

Many bacteria, fungi and viruses naturally live on our skin and inside us, including in both small intestinal and in the large intestine (colon). They contribute in big ways to human health and wellness, such as protecting us against infections, maintaining healthy immune systems, and improving food digestion.

Probiotics have several proven effects:

  • They increase the numbers of 'healthy' organisms in your gut (digestive tract) and reduce the numbers of the organisms that could be harmful.

  • They strengthen the barrier in the gut to harmful substances.

  • They promote a more healthy immune system in the gut which might make it more sensitive.

  • They help our bodies to absorb important nutrients from the gut, such as short chain fatty acids.

  • They lessen the amount of inflammation in the gut, although the significance of this is not fully understood.

  • They reduce the number of episodes and severity of diarrhoea - this is the main reason that probiotics are prescribed.

However, many claims are made for the health benefits from taking probiotics and prebiotics, which are not supported by evidence. In several countries manufacturers of probiotic-containing yoghurt have had to drop exaggerated claims that it boosted immunity and aided 'intestinal rhythm'. The worldwide probiotic market was said to be worth US$35 billion in 2015 and is expected to grow rapidly in the coming years.

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Probiotics for diarrhoea caused by antibiotics

One of the side-effects of some antibiotics is diarrhoea, caused by removing all the healthy bacteria in your gut - so-called antibiotic-associated diarrhoea. The most severe type of antibiotic-associated diarrhoea is due to a germ (bacterium) called Clostridium difficile (often shortened to C. diff).

C. diff can thrive and multiply when the healthy gut microbes have been removed. There is good evidence that probiotics can prevent antibiotic-associated diarrhoea in children and adults who are taking antibiotics. There is also good evidence that they prevent C. diff-associated diarrhoea, although the best strain and the best dose are not yet known.

See the separate leaflet called Clostridium Difficile (C. Diff) for more information about this condition.

Probiotics for irritable bowel syndrome

Irritable bowel syndrome (IBS) is a very common condition that causes frequent attacks of tummy pain, bloating and either constipation or diarrhoea. Probiotics have been shown to be an effective treatment for IBS, although it isn't clear which strain of probiotic or what dose works best.

See the separate leaflet called Irritable Bowel Syndrome for more information.

Probiotics for children

Do probiotics prevent colds and stomach bugs in children who go to nursery?

There is some research that suggests probiotics might reduce the number of 'coughs and colds' (respiratory tract infections) in children who attend day nursery but the research isn't very convincing and is only for LABs. There is no evidence that probiotics can prevent stomach bugs in young children.

Do probiotics prevent allergy in children?

They are not recommended to prevent allergies. This is because, although probiotics taken by the mother when she is pregnant and by the baby once born may reduce the chances of developing atopic eczema, they may also increase the risk of developing wheezing and allergic rhinitis.

Do probiotics help in the treatment of diarrhoea in children?

Yes. In research that included almost 2,500 children, treatment with a specific type of LAB probiotic (in addition to normal treatment) was shown to shorten the number of days that a child had diarrhoea for by a day.

See the separate leaflet called Acute Diarrhoea in Children for more information.

Do probiotics help children with tummy pain?

Tummy (abdominal) pain is very common in children and they can sometimes get it repeatedly. It isn't clear whether or not probiotics might help, as so far the research isn't of good enough quality.

See the separate leaflet called Recurrent Abdominal Pain in Children for more information on this problem.

Do probiotics help in baby colic?

There is some research that suggests a particular type of LAB (Lactobacillus reuteri DSM 17938) may help with the treatment of a baby who gets colic, but only if they are fully breastfed. There is very little research on using probiotics to prevent colic.

See the separate leaflet called Baby Colic for more information.

Probiotics for women

Do probiotics treat or prevent vaginal infections?

Bacterial vaginosis (BV) and vaginal thrush are the two most common infections that women can get in their vagina. Researchers are looking at whether using probiotics (either swallowing them or using them internally put into the vagina) might be effective in treating or preventing these infections. Both of these infections depend on the normal microbes that live in the vagina being reduced, so it is possible that probiotics might help but so far the results are unclear.

You can read more about both of these conditions in our separate leaflets called Bacterial Vaginosis and Vaginal Thrush (Yeast Infection).

Do probiotics prevent urine infections (cystitis)?

Many women will have a urine infection at some time in their lives but a few women will get one again and again. There are studies looking at whether probiotics might reduce the chance of having a recurrent urine infection but unfortunately the studies are of poor quality. The authors of a review published in 2015 concluded that a benefit could not be ruled out.

See the separate leaflet called Recurrent Cystitis in Women for more information.

Probiotics in pregnancy

Women of childbearing age are one of the most common groups to take probiotics and prebiotics as food supplements. In the Netherlands, almost one woman in every seven pregnant women takes them.

It has been suggested that probiotics might reduce the chances of having a baby who is born too early (premature labour). Unfortunately, this has not been proven and research has shown that probiotics and prebiotics neither increase or lessen the risk of having a premature labour, nor affect any other events of pregnancy.

Probiotics have also been taken by pregnant women to reduce the risk of their baby developing allergies. As explained above, this is not recommended.

Probiotics and weight loss

If you are overweight or obese this can be for many different reasons but overall it is due to having taken in more energy, in the form of food and drink, than you have used up by being active. However, researchers have identified a link between the microbes in a person's gut and the likelihood that they are overweight or obese.

What is not clear though is whether the different gut microbes are the cause of the weight gain or just the result of the diet that itself caused the weight gain. So, will probiotics help you to lose weight? For the moment, the answer is no, probably not.

You can read more about how to lose weight in the separate leaflet called Weight Loss (Weight Reduction).

Probiotics and cancer

Cancer of the colon is a very common cancer that may be linked to our diet. Researchers have suggested that probiotics and prebiotics might help prevent colon cancer but so far the research proving this is very limited.

Diarrhoea is a common side-effect of radiation to the tummy (abdomen) used to treat some cancers. Probiotics may be helpful in preventing and treating this effect of radiotherapy on the gut.

Are probiotics and prebiotics safe?

It is important to know that no research has been done specifically to look at the safety of probiotics and prebiotics. However, in general, both probiotics and prebiotics are considered safe, except in rare situations such as when someone is critically ill or for a premature baby.

There are some concerns that probiotics may help bacteria to develop resistance to antibiotics, and the long-term safety of probiotics is not known.

The quality of probiotics depends on the manufacturer and, since most are not manufactured as medicines, they do not have to satisfy the much stricter criteria for the regulatory standards of medicines. There are concerns regarding many commercially available products - a review showed several problems:

  • Products were often mislabelled and did not contain the strain of microbe they were said to contain.

  • Some contained potentially harmful microbes.

  • Quantities of live microbes were so low in some products that they could not have any effect.

This issue needs to be resolved by the regulatory agencies.

Note: you can't assume that probiotic foods, such as yoghurts, and food supplements bought in the shops will have the same effects as the probiotics used in the studies discussed above, which used medicine-grade probiotics of specific strains and doses.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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