Probiotics: what are they and how can they help?

22nd February, 2022 • 8 min read

Probiotics are ‘friendly' live bacteria and yeasts of the same kinds that naturally live in your gut, as well as your mouth, skin, lungs, vagina (if you have one) and urinary tract. They’re sold in supplement form or added to certain foods, like kombucha, tempeh and kefir. But they’re also naturally present in some foods, like miso, cottage cheese and buttermilk.

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There’s already some evidence in this exciting area of gut health, to show that probiotics can help your body maintain a healthy balance of ‘good’ and ‘bad’ bacteria in your digestive system to keep your gut healthy. There’s also some evidence that probiotics can help symptoms in certain conditions, but more research is needed in this area. This is partly due to the many different types of bacteria that exist and their various strains.

So could they help you? Keep reading to find out everything you need to know about probiotics, including what they are, whether they can help you and your condition, and how to use them in the right way.

Why does your gut need ‘good’ bacteria?

Your gut has trillions of bacteria, fungi and other microbes living in it – some are good while others are bad for your health. Having a healthy gut means you have an even balance of ‘good’ and ‘bad’ bacteria, which allows your body to fight off illness, infection and inflammation.

Your body usually makes its own ‘good’ bacteria or uses the foods you eat to grow more to keep this colony of bacteria and yeasts in balance – you might hear it described as your gut microbiome.

When it comes to the specific kind of probiotics that may help keep this healthy balance, these 2 are the most common:

  • Bifidobacteria (B.) – studies suggest that some strains may help reduce the growth of ‘bad’ bacteria and produce the enzyme lactase, that helps break down the sugar lactose (commonly found in milk)
  • Lactobacillus (L.) – studies suggest they also help break down lactose and produce lactic acid, which may keep ‘bad’ bacteria in check

Other probiotic species include Saccharomyces, Streptococcus, Enterococcus, Escherichia and Bacillus.

Within these species of probiotics are a number of strains, and each can have a different effect on the body. On probiotic product labels, you’ll often see species names listed alongside the strain name, such as L. acidophilus or B. animalis.

How do probiotics work?

At the moment, scientists think probiotics in foods and supplements may work by helping balance out your ‘good’ and ‘bad’ bacteria, restoring your body’s natural balance when it’s been knocked out of kilter. This could be after an illness. It could also be after taking

, which wipe out the ‘good’ as well as the ‘bad’ bacteria while treating an infection.

Foods to keep your gut healthy

It’s thought you may be able to improve or maintain the levels of ‘good’ and ‘bad’ bacteria in your gut by eating probiotic-rich foods every day. More research is needed to help us understand how much you need to eat to see results.

The most effective probiotic foods are thought to be:

  • yoghurt (especially plain Greek yoghurt) – yoghurt products with ‘live cultures’ (also known as ‘active cultures’) have probiotics in them. But people with
    lactose intolerance
    may get uncomfortable tummy symptoms after eating yoghurt, such as
    gas (flatulence)
  • kefir, a tangy drink – research suggests kefir contains higher concentrations of ‘live cultures’ than yoghurt does, and it’s thought it may be a more effective probiotic because it can better resist the acidic environment of your gut
  • fermented vegetables – these include pickles, kimchi and sauerkraut

Read more about

stomach-friendly foods

Find useful information on other areas of gut health with our

complete Healthy Gut Guide.

Which probiotics may help your gut problem?

If you’ve got a specific gut problem, from

irritable bowel syndrome (IBS)
, taking a probiotic supplement may be an option for you to try.

In the UK, supplements are normally available from pharmacies, health shops and online, but sometimes, they’re prescribed in specific circumstances by specialists like gastroenterologists. Before you start using these supplements, it’s best to get advice from a doctor.

Some conditions that science tells us may be improved with probiotics include:

  • IBS – some small studies suggest these supplements may help relieve symptoms like bloating
  • Clostridium difficile infection – when the bacteria
    Clostridium difficile
    infects the large intestine of people who’ve been taking antibiotics for a long time, it can cause diarrhoea. Some studies have started to show that some probiotic supplements may be able to reduce the risk of getting this specific diarrhoea in this group of people
  • antibiotic-associated diarrhoea – taking the probiotic strain L. acidophilus at the same time as antibiotics may help reduce the likelihood of antibiotic-associated diarrhoea, especially in young and middle-aged people. The probiotic strain B. animalis is also thought to protect against diarrhoea and reduce the
    side effects of antibiotics
  • constipation
    – some studies suggest that products containing Lactobacillus or Bifidobacterium may help constipated adults poo more regularly, but effectiveness varies from study to study. There’s also some evidence that the strain B. longum may help you poo more often if you’re constipated
  • diarrhoea caused by cancer treatment – some research suggests that certain probiotic supplements may help prevent or treat diarrhoea caused by
  • inflammatory bowel disease (IBD)
    – an umbrella term for conditions that cause the digestive system to become inflamed, resulting in symptoms like diarrhoea and tummy pain. Some early studies show that adding some probiotics to other treatment methods, such as medication, could help treat an IBD condition called
    ulcerative colitis
  • travellers' diarrhoea
    – a small number of studies appear to suggest that some probiotics may help prevent traveller’s diarrhoea. More research is needed into what strains may be most effective

How to get the most from probiotic supplements

Probiotics in supplement form can be taken as capsules, powders or liquids, and each often contains a mixture of different probiotic strains in differing doses.

Probiotic supplements sold in shops and online don’t need to follow strict approval processes because they aren't considered to be medicines.

We’d always recommend speaking to a pharmacist or a doctor before taking a probiotic supplement, but the following steps may help you select the best-quality product and potentially get the most from it.

  1. Look for ‘live’ or ‘active bacterial cultures’ on the product label.
  2. Consider choosing products that have at least 1 billion colony forming units (CFU) on the label – studies suggest this is the minimum amount of quality bacteria needed to make a difference.
  3. Choose products containing the Lactobacillus species – this species is thought to be the most resistant to stomach acid.
  4. Take the supplement as recommended on the instructions – different species and strains, how often you’re taking it and what you’re taking it for can have an impact on its effects. Some probiotic products should be taken on an empty stomach and 30 minutes before food, while others need to be taken with food.
  5. You may want to choose a probiotic that also contains prebiotics – this is called a synbiotic. Prebiotics are special plant fibres that act as food for probiotics. If taken regularly, it's thought that both can work together to maintain healthy levels of ‘good’ gut bacteria, but more research is needed.
  6. Too much heat can kill the bacteria – store your probiotics in a cool, dry place to allow the ‘live’ bacteria to thrive. Some probiotics need to be kept in the fridge though – check storage instructions if you’re unsure.

Side effects of probiotics

Most healthy people can take probiotics in both food and supplement form safely, without noticing any side effects. You should always check the label and talk to a pharmacist or doctor before taking supplements if you’re

or breastfeeding.

In rare cases, you might notice a reaction in the first few days, but this will usually go away on its own. Symptoms may include:

  • an upset tummy
  • diarrhoea
  • bloating
  • gas (flatulence)

In certain people, taking probiotic supplements might cause infection. This could be the case if you have:

  • a weakened immune system (including if you’re going through chemotherapy)
  • a critical illness
  • recently had surgery

You should speak to a doctor before considering probiotics if this is the case. Read more about

whether probiotics are safe for everyone

When to see a doctor

You should see a doctor if you’ve been taking probiotics which are making your symptoms worse or giving you worrying symptoms.

You should also see a doctor if you:

These could be signs of an underlying health condition, so book an appointment with a doctor if you have any of them.

Try our

Smart Symptom Checker
to get more information about your health.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.