Probiotics, Prebiotics & Gut Health: A Pharmacist’s Guide

By Lauren O’Reilly, Pharmacist 

Gut health has become one of the biggest topics in wellness, and probiotics are everywhere, from capsules and powders to being mentioned in our yoghurts and yoghurt drinks. 

But do you actually need one? 

As a Pharmacist, this is something I get asked about so often, so I’m going to break it down for you here. 

I think probiotics are an area where more isn't necessarily better. Some specific strains have evidence for supporting gut health in particular situations, while there isn't good evidence that everyone needs a generic daily probiotic. 

Before looking at supplements, it's worth understanding what probiotics and prebiotics actually are, and how much of both you can get from your diet. 

A note on the terminology 

You’ll see the terms “probiotic” and “prebiotic” used throughout this article because they are widely used scientific terms for discussing microorganisms and the food components that interact with them. 

However, under EU food law, FSAI considers “probiotic” and “prebiotic” to be health claims, and there are currently no authorised health claims for probiotics or prebiotics. This is why you may see products using alternative wording such as “live cultures” or referring to the specific microorganisms or ingredients they contain. 

Here, I’m using these terms to explain the science and help you understand the terminology you’ll commonly come across when researching gut health. 

Probiotics and prebiotics do different jobs 

Probiotics are live microorganisms which, when consumed in adequate amounts, can provide a health benefit in specific circumstances. 

Prebiotics are certain types of food components that are used by microorganisms in the gut, helping to influence the composition or activity of the gut microbiota, essentially feeding the live microorganisms or beneficial bacteria that live in your gut. 

A simple way to remember it: 

Probiotics = live microorganisms 

Prebiotics = food for microorganisms 

You can get both through food. 

Not every fermented food is technically a probiotic, as this depends on the microorganisms present and whether they remain alive in the finished product. 

For most people, however, eating a varied diet containing plenty of fibre and different plant foods is an excellent starting point for supporting a healthy gut microbiome. 

Why some probiotics work, and others may not 

The word “probiotic” can make products sound interchangeable or equal, but they're not. 

Different products contain different microorganisms, species and strains. Research showing a benefit from one particular strain can't automatically be applied to every probiotic on the shelf. 

That's why I wouldn't choose a probiotic simply because it contains the highest number of bacteria. CFU, or colony-forming units, tells you how many viable microorganisms are provided, and is the number usually in denominations of billions on the box. It is important to note that a bigger number doesn't automatically mean a better product. 

The World Gastroenterology Organisation recommends considering the evidence for the specific strain and the specific situation when deciding whether a probiotic is appropriate. 

There's also an important Irish regulatory point: there are currently no authorised health claims for probiotics or prebiotics under EU food law. This doesn't mean that research into probiotics doesn't exist; it means we need to be careful about making broad claims about what a probiotic can do. 

Choosing a probiotic: what I look for 

If you're considering one, I'd focus on these rather than the marketing on the front of the packet. 

1. Have a reason for taking it 

A targeted probiotic may be more appropriate in some specific situations than simply taking one indefinitely and non-specifically for “gut health”. 

2. Look at the strains 

Ideally, the label should identify the genus, species and strain. This allows you to assess whether there is evidence for that particular microorganism rather than relying on the word “probiotic” alone. 

3. Check the dose and storage instructions 

Different products have different recommended doses, and some require refrigeration while others are designed to be stored at room temperature. Follow the manufacturer's instructions. 

4. Give it a reasonable trial 

You don't necessarily need to take a probiotic forever. If you're using one for a particular reason, follow the recommended course or the advice of your healthcare professional. If you've been taking one for months without noticing any difference, it's worth reassessing whether you actually need it. 

Beneficial Bacteria Supplements: Which approach makes sense for you? 

Millies stock several products that take different approaches to gut and microbiome support. They aren't interchangeable, so I'd choose based on what you're actually trying to achieve rather than simply choosing the product with the highest CFU number. 

 A note on these supplements: These products take different approaches to gut and microbiome support and are not interchangeable. Food supplements should not be used as a substitute for a varied, balanced diet and healthy lifestyle. Always follow the recommended daily intake and check with your pharmacist or GP before taking a supplement if you are pregnant, breastfeeding, have a medical condition or take medication. 

“Can you take probiotics every day?” 

This is something I’m asked often as a Pharmacist. 

For most healthy people, probiotics are generally considered safe for daily use, although some people can experience temporary bloating or digestive changes when starting them. 

Daily use isn't essential for everyone. Your long-term diet is far more important than whether you remember to take a probiotic capsule every morning. 

People who are seriously unwell or immunocompromised should speak to their doctor before taking probiotic supplements, as rare but serious infections have been reported in vulnerable individuals. 

Your diet is a very important part of the equation 

One of the easiest ways to support your gut microbiome is to increase the variety of plants you eat. 

Think vegetables, fruit, wholegrains, beans, lentils, nuts and seeds, and even spices (yes, spices count!). Different plant foods provide different types of fibre and other compounds that interact with the gut microbiota. 

If your current diet is low in fibre, increase it gradually. Suddenly adding large amounts of beans, lentils or fibre supplements can cause bloating, so give your digestive system time to adjust and make sure you're drinking enough fluid. 

You don't need an expensive powder to start. Adding oats to breakfast, beans or lentils to meals (I always add a tin of green lentils to a bolognese, and hardly notice it!), onions and garlic when cooking, and trying a wider variety of vegetables throughout the week can make a meaningful difference to the overall quality of your diet. 

And don't forget fermented foods. 

Live yoghurt and kefir can be useful additions to your diet, and some fermented foods contain live microorganisms. Add yoghurt to your porridge, and nuts and seeds to your salads and dinners, and put some kimchi or sauerkraut on the side of your dinner or lunch plate for a tangy addition. 

When gut symptoms need investigating 

A probiotic shouldn't be used to mask persistent or unexplained digestive symptoms. 

Speak to your GP if you have ongoing changes in bowel habit, persistent abdominal pain or bloating, blood in your stool, unexplained weight loss, persistent diarrhoea or constipation, or symptoms that are new or concerning you. 

The answer isn't another supplement - it's finding out what's causing the symptoms in the first place, and getting the right advice from there. 

As Millie's resident pharmacist, my advice is to choose a probiotic for a reason and only when appropriate for you, not simply because it's the highest strength or the most heavily marketed. 

A note on probiotics 

If you're pregnant, immunocompromised, seriously unwell, have an underlying medical condition or are giving probiotics to a child, speak to your GP or pharmacist before starting a supplement.