What are Probiotics?

Dr Kate Stephens PhD Food and Microbial Sciences; Gut Microbiology (University of Reading), BSc Medical Microbiology

The digestive tract is home to trillions of microorganisms, collectively known as the microbiome. Some of these are good for us, some are harmful and some are neutral. Disruptions to the good bacteria in the gut can compromise our health. The resulting imbalance of good and bad bacteria is known as ‘dysbiosis’ and can result in poor digestion, lowered natural immunity and a large variety of conditions, read more about this here: Gut Health - All You Need To Know

probiotic strains under the microscope
Probiotic strains under the microscope - from left to right: B. lactis BB-12, L. acidophilus LA-05 and B. infantis Rosell-33

You may have heard the terms 'probiotic' or 'probiotics' and wondered about their meaning. 'Probiotic' actually means 'for health, and probiotics, such as acidophilus, are microorganisms that are thought to offer benefits to their human host. But what are probiotics good for? The main benefit of probiotics, also known as 'good bacteria', 'friendly bacteria, or 'live cultures', is to crowd out harmful bacteria in order to keep the gut healthy. With around 70% of your immune system based in your gut, gut health is a key factor to our overall wellbeing.

Probiotics are also known as friendly or good bacteria. But if we're being specific, it's worth pointing out that some probiotics are actually yeasts!

Covered in this article:

  • Probiotics are the friendly bacteria and yeasts that can be beneficial for our health.
  • The gut microbiome is the collection of friendly bacteria and yeasts that naturally live in our gut and play an important role in various aspects of our health including our gut health, immune health and skin health.
  • Probiotics can be taken in supplement form and they can also be found in fermented foods and drinks.
  • It is important to know the probiotic strain in your supplement to ensure that the properties of that strain are suitable for you.

What do probiotics do?

Probiotics are thought to support immunity by stimulating the body’s natural defences, and by lining the intestines with a protective layer of friendly bacteria that bars pathogenic substances in the gut from harming the body. As two-thirds of the body's immune system is managed in the gut, it may be important to keep one's probiotic levels high.

Research shows that probiotics support digestive health by producing specific enzymes needed in the digestion of food and aiding the breakdown of foods substances.

Probiotics are also believed to improve the absorption of vitamins & minerals into the bloodstream, and even produce B complex vitamins & vitamin K. Read more about how probiotics work.

What are probiotic strains?

Not all probiotics are the same. Research shows that different probiotic strains have different benefits and can help support different areas of health, read more about this here: Are all probiotics the same?

 But what exactly is a strain? A strain denotes a type of bacteria - and informs us on a very specific, in-depth level (more specific, than a species, for example). Take a look at the image below to understand the context of genus, species and strain.

Diagram explaining genus, species and strain. Probiotics Learning Lab

GENUS: A genus is a biological classification of living organisms. The term comes from the Latin genus meaning group. A genus contains one or more species. Examples of common probiotic genera include Bifidobacterium and Lactobacillus.

SPECIES: ‘Species’ refers to a type of microorganism existing within a genus or family. For example, acidophilus is the name of a species within the Lactobacillus genus.

STRAIN: A probiotic ‘strain’ is a genetic variant or subtype of a species. Different probiotic supplements contain different strains, which may be classified under the same species and genus. However, one acidophilus is not equal to another acidophilus. It’s the strain level that matters when you choose a probiotic in order to help with a specific health condition. If you're looking to take a probiotic, make sure to look out for robust, well researched strains when choosing the right for you.

Diagram to explain strain break down

After all, when choosing a dog there is a difference between embarking on life with a Labrador or a Dachshund.

What’s the difference between Probiotics and Prebiotics?

Whereas probiotics are the beneficial microorganisms themselves, prebiotics are a source of food for probiotics and help them grow, multiply and survive in the gut. For more information, take a look at our article What are Prebiotics?

What are probiotic foods?

Foods and drinks that naturally contain probiotics or live cultures are those that have been fermented. Foods that are fermented go through the process called lacto-fermentation in which the natural bacteria feed on the sugar and starch creating lactic acid. This process was originally used for food preservation as it stops the food from spoiling, and creates beneficial bacteria, b-vitamins, and enzymes. Foods or drinks that contain these beneficial live cultures are:

  • Kombucha
  • Kefir
  • Miso
  • Tempeh
  • Sauerkraut
  • Live probiotic yoghurt
  • Kimchi
  • Sourdough
  • Some cheeses

Don’t know where to start with fermented foods? Read our Top 5 Fermented Foods (& Recipes!)

Although fermented probiotic foods or probiotic drinks make a great addition to any diet, it is hard to know what exact probiotic strains are in these natural foods. If you are looking to support a certain symptoms or health condition with probiotics, then it is best to choose a strain researched for the condition you are looking to support. Read more about this here: Fermented Foods vs. Probiotics

Probiotics and health concerns

The Probiotics Database provides more detailed information on some of the most researched strains in the world, and explores the clinical research behind different strains, for different circumstances. Health practitioners can view the Probiotics Database on the Professionals site. When it comes to research on probiotics, generally speaking, the bulk of the gold-standard clinical trials suggest that probiotics can help to support gut health, for example, helping to prevent antibiotic-associated diarrhoea. However, emerging fields of research include a huge variety of health concerns, such as weight loss, skin health and even mental health. Research into probiotics is growing at an exponential rate - so probiotics remain an exciting field to watch.

Is there a difference between live cultures and probiotics?

Whilst live cultures and probiotics are often used as synonyms, strictly speaking, they are not exactly the same thing. We love live cultures and fermented foods and drinks such as yoghurt, kimchi, kombucha and kefir. However, if we take the definition that probiotics are microorganisms that are proven to have health benefits on the human body, then it's worth pointing out that live cultures found in foods and drinks are not usually clinically trialled, and therefore cannot be linked to a specific health benefit. As mentioned earlier, there is also rarely a guarantee of the types or numbers of live cultures found in fermented foods. It may therefore be more accurate to refer to most fermented foods as containing 'live cultures’ and reserve the term 'probiotics' for foods and supplements that have been clinically studied in humans and proven to have health benefits. For more information on this topic take a look at the Food Myth.

Is it OK to take a probiotic every day?

Yes, it is perfectly fine to take a probiotic every day. Years gone by, fermented foods or drinks like yoghurt would have been central to our daily diet. Taking a probiotic supplement is just the modern way of consuming these foods, but you are also selecting the types of strains too. Read more about this here: Can I take probiotics every day?

Which is the best probiotic?

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. Choosing the right one should depend on the specific health concerns you have, as different types of probiotics have been shown to help support different areas of health.

Diagram of gut and bacteria. Probiotics Learning Lab.

To summarise the key points:

  • Probiotics are microorganisms that offer health benefits.
  • Probiotics can support immunity, digestive health and make enzymes and vitamins.
  • Probiotics are made up of a genus, species and a strain and are all very different.
  • Probiotics in foods and drinks are beneficial, but we rarely know the strains or amounts.
  • The best probiotic supplement for you depends on the condition you are looking to support.

Read more about:

The Gut-Brain Axis

For more in-depth information about probiotics, see:

Researching Probiotics: Our Tips

Human Strain

This article was last updated on 25.03.2021