• Arthur

What’s the difference between probiotics and prebiotics?

Updated: May 21



The ‘P’ words have been thrown around a lot on social media, food marketing and news coverage (well maybe less since coronavirus has taken over the spotlight). So what’s so special about probiotics and prebiotics? Why have they suddenly made it to the lime light?

A major reason why these terms are becoming more and more mainstream is because of the increased scientific research surrounding them. There’s a growing body of research investigating the gut microbiome to determine if there are significant ways to alter it to improve human health. In order to determine a ‘cause and effect relationship’ that then can be used to guide recommendations for human health, all other factors and variables need to be accounted for that could potentially be causing the ‘effect’ or benefit. In short, the results need to conclude that the received probiotic or prebiotic was the variable causing the ‘effect.’ Make sense ? If not, (or if you are feeling like nerding out) check out more on the science behind gut health.

Right, so let’s get back to probiotics and prebiotics. According to the International Scientific Association for Probiotics and Prebiotics (ISAPP), probiotics and prebiotics are defined as follows:

Probiotics - ‘microorganisms, that when administered in adequate amounts, confer a health benefit to the host.’

Prebiotics –‘a substrate that is selectively utilised by host microorganisms conferring a health benefit.’

So in other words, probiotics are the microorganisms themselves, whereas prebiotics are the food that microorganisms feed upon (hungry little buggers!).

Let’s start with probiotics:

Sure there might be live bacteria in unpasteurised foods like yoghurt, kefir, kombucha, sauerkraut, kimchi, etc., but that doesn’t necessarily mean they are probiotics. In some cases these foods might have bacteria that share some characteristics with well-studied probiotic strains and show promise for future research, but they are NOT classified as probiotics. Despite the lack of evidence, many commercial enterprises are super quick to capitalise on these terms. As a result you often see products on the market that use terms like probiotic or prebiotic in their marketing.


We hate to be the bearer of bad news, but oftentimes these marketing messages are misinformed and unsubstantiated. In the UK legally the term ‘probiotic’ cannot even be displayed on product packaging. This is due to the lack of scientific evidence available right now for making those claims. It’s also put in place to protect the consumer (that’s YOU!) from purchasing a product under the pretence that the product will provide health benefits in some way. According to the definition above, for microorganisms to be classified as a probiotic is no easy feat! I’m not going to get into it too much here, but if you want to learn more, read about why fermented foods are not probiotics HERE .

How about prebiotics?

Fermented foods like, sauerkraut, kimchi, tempeh and other plant based ferments often provide a source of dietary fibre. But just because it’s ‘fibre’ doesn’t necessarily mean it’s a prebiotic. Let me explain; in general, dietary fibre is a series of compounds that bypass digestion in our stomach and small intestine and instead reach our large intestine mostly intact and are then feasted upon by the bacteria that reside there. As a result of eating fibre, bacteria in our large intestine produce by-products that are then either consumed by other native bacteria in our gut, utilised by our bodies in some way or simply just excreted.

The same is true for prebiotics. These are specific types of compounds that have been shown to be utilised by certain species of bacteria. As a result, these bacteria may produce metabolites that are associated with human health. IMPORTANT NOTE: even if you ate a food containing prebiotics there is no guarantee of associated health benefits (sound familiar?). This is because the bacterial ecosystem within each and every one of us is HUGELY complex. With microorganisms competing for food, cross-feeding between species and lack of certain microorganisms that can break down complex prebiotic molecules, the outcome for that wee prebiotic you ate is mostly uncertain.


And it can be even more uncertain in fermented foods! This is because of the process of fermentation itself; for example, if you were to make sauerkraut with vegetables that contain a source of prebiotics (garlic, onions, leeks – to name a few) and then let it ferment on your counter for a couple of weeks, it’s entirely possible that the microbes within your countertop sauerkraut may have already broken down these prebiotic fibres. Thus when the sauerkraut is ready and you begin to scarf it down, there is significant uncertainty about how much of those prebiotic fibres are left intact! See, this s**t is complicated.

Buuut prebiotic containing foods are super nutritious anyway and you might already be consuming them unknowingly!

Common foods that contain prebiotics are: - Artichokes (Jerusalem & globe) - Onion - Asparagus - Garlic - Bananas (the greener = the higher resistant starch) - Whole grains like barley & oats

Now don’t just be eating these foods! Remember, variety is key to a healthy body, mind and microbiome.

Some other stuff to consider.


Before you head off on a shopping spree for all things fermented, probiotic and prebiotic, make sure you equip yourself with knowledge beforehand. If you’re an individual interested in some of the benefits probiotic pills may offer, then some options are to check out the ISAPP website or ask your GP. The ISAPP website list probiotic strains that have been well-studied and used to manage certain ailments. Not all probiotic pills and strains will offer you benefits specifically. It’s important to find the right one that works for you and sometimes the only way to achieve this is through trial and error.


One of the downfalls of probiotic pills is they tend to only contain a single strain or just a couple of different strains of bacteria, whereas fermented foods likely contain many more (but again, are largely understudied). If you’re keen on getting live microbes from food, then go with fermented foods like kimchi, sauerkraut , kombucha, yoghurt and kefir. Just make sure you get them from the refrigerated section, as the products found on the shelf are often pasteurised. In regards to prebiotics, I wouldn't bother with supplements. There are plenty of foods out there that naturally contain prebiotics. Aim to include them into your diet daily.

We can ALL get the most out of fermented foods not just because of the live bacteria within them, but because they’re nutritious, damn delicious and add diversity to our diets- one of the only scientifically proven ways of altering our gut microbiome.

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