What are probiotics and what do they do?

What are probiotics and how do they work?

A probiotic is a live microorganism that confers a health benefit when administered in adequate amounts.

Many of these live micro-organisms occur naturally in cultured or fermented foods such as yogurt, kimchi, sauerkraut, miso and kefir. They are known as ‘good’ or ‘friendly’ bacteria as they compete for space and food with less beneficial – and even harmful – microbes and prevent them from settling in the gut.

Check out the top 10 probiotic foods to support your gut health.

What are prebiotics and how do they work?

Prebiotics are non-digestible carbs. Just as their name suggests, we can’t digest them, but they’re broken down by microbes in the gut and act as fuel to nourish the microbes that live in our colon. These carbs occur naturally in the diet and are found in many foods including garlic, bananas, oats, onions and leeks.

What are synbiotics and how do they work?

A synbiotic is the term given to a combination of probiotics and prebiotics. This means that along with the friendly microbes, there is also a food source. Taking a synbiotic improves the chance that the microbes will survive and thrive in the gastrointestinal tract. Synbiotics are available in supplement form – on the label you might see bacterial varieties such as Lactobaccilli, Bifidobacteria spp combined with a prebiotic, such as inulin or fructo-oligosaccharide.

Why it’s important to look after our gut bacteria

The microbial balance of our gut changes over time which can impact our health and wellbeing. There are a number of lifestyle and dietary factors that may negatively affect our gut balance, these include:

• High levels of stress – this may change the number and diversity of gut bacteria, which in turn may affect your immune system
• Excessive alcohol consumption – this can be inflammatory and affect the lining of our digestive system, this negatively impacts the beneficial microbes that live there
• Smoking – can have a negative impact on our gut microbes as well as the other well-documented health risks it presents
• Antibiotic use – although designed to fight infections, antibiotics reduce and deplete the microbes living in the gut, this can disturb the natural balance
• Following a low-FODMAP diet, which reduces your intake of fermentable carbs, this can negatively affect the microbes in the gut. It is therefore important that these foods are omitted for a specified time and only under the guidance of a specialist dietitian.

What are the different types of probiotics?

There are numerous types of probiotics, each with their own unique characteristics. They are available as supplements in powder, tablet or liquid form, and the different strains of microbes may be combined with others or appear on their own. How these benefit you will depend on the relative balance of your existing microbes, and will be unique to you.

When choosing a supplement, it is the strain of bacteria that matters, especially if you are hoping to help a specific health condition. If you are looking to take a probiotic, make sure you look for robust, well-researched strains. For example, some strains of Lactobacillus acidophilus have been clinically shown to lower the incidence of antibiotic-associated diarrhoea.

How do I know what strain a probiotic is?

It is easy to get confused when talking about probiotics – this is because you may hear them referred to as a species or a strain. The following is how probiotics are classified and how you are likely to see them described on labels:

• Genus (family or group) – Lactobacillus
• Species (a type of micro-organism within the family or group) – Lactobacillus acidophilus
• Strain (a genetic sub-type or variant within that species) – Lactobacillus acidophilus Rosell 52

In our example Rosell 52 is the strain of Lactobacillus acidophilus bacteria – this strain is well-researched and has numerous benefits including helping to reduce stress-induced stomach upsets.

What are the health benefits of probiotics?

There is still much to discover about how the microbes in our gut influence our health, although it is already well-proven that probiotics improve IBS symptoms, traveller’s diarrhoea and the duration of antibiotic associated diarrhoea.

Other potential benefits include lowering blood pressure, improvements to the immune system, the potential to improve cholesterol levels and benefits in cold or flu during stressful periods.

What are the risks of probiotics?

Generally, probiotics are safe for healthy individuals, however those with a compromised immune system should seek advice from a specialist dietitian or GP.

What should I look for when choosing a probiotic supplement?

Choosing a supplement appropriate to your circumstances can be tricky given the vast number on the market, here are some of the main points to consider:

• Check the label for the number of colony forming units (CFU) for each bacterial strain - this tells you how many bacteria per dose. If you’re taking the product for a specific health issue, check the CFU per dose is consistent with the amounts used in any relevant clinical trials.
• Choose a product that guarantees the CFU up to the product’s expiry date.
• Check how the product needs to be stored e.g. liquid products, including dairy, are the least shelf stable and may need to be refrigerated. Probiotics in solid form, such as capsules and powders, are more stable and can be stored for a longer period of time.
• Multi-strain products may offer more benefits but the important thing is that there are adequate CFUs per strain to be effective.
• The acidic environment of the stomach can reduce the efficacy of a probiotic supplement – so look for a product that has a hard capsule shell to protect the microbes or provides controlled release to the desired location of the gut (colon). Examples include Alforex, Symprove and VSL #3. Each of these is designed to treat specific 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 otherwise, probiotics should be taken for a minimum of twelve 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, ask for help from a specialist. There are so many products available on the market it can be difficult to decide which to choose. Whether it’s a powder, tablet or drink you’re looking for, choosing the right one should depend on the symptoms you’re experiencing. In order to maintain gut health, we should all include a variety of plant foods in our diet as well as fermented foods such as yogurt labelled ‘contains live cultures’, kefir or kimchi.

Speak to your GP if you're experiencing symptoms or if you're considering starting a supplement.

Find out more...

How does diet affect gut health?
What supplements should I take?
Top 12 healthiest fermented foods
Top 15 probiotic foods to support gut health
Top 7 health benefits of fermenting
Top 10 health benefits of kefir
Gut-friendly recipes

This article was reviewed on 27 August 2024 by Kerry Torrens.

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.

Kerry Torrens is a qualified Nutritionist (MBANT) with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including Good Food.

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