What is the difference between probiotics and prebiotics?

This is a question that we’re often asked. With such similar-sounding names, many people assume that probiotics and prebiotics are one and the same, but there is a very subtle difference between them. One refers to the beneficial gut bacteria themselves, the other is the food that they need to thrive. So… which is which?

The lining of your gut, like every surface of your body, is covered in microscopic microbes, mostly bacteria, known as the microbiome.

The key to a healthy microbiome is maintaining balance among the nearly 1,000 different species of bacteria in your gut and there are two primary ways to help maintain this balance:

1. Helping the microbes already there to grow by giving them the foods that feed them – prebiotic fibres, and
2. Adding living microbes directly to your system – friendly bacteria (probiotics).

Probiotics = Friendly Bacteria 

Probiotics are proxies for the ‘friendly’ microorganisms – live bacteria and yeasts – that populate the digestive tract and can help support the health of the digestive system. They are bacteria that are consumed through food and supplements and are strains found naturally in our intestines (primarily

The gut microbiome is a highly complex and dynamic community of microorganisms, most of which are bacteria, and more than 1,000 different species/strains of bacteria have been identified with enough frequency to be considered a ‘normal’ part of the human microbiome.

The overall relationship of the microbiome to our body is both favorable and beneficial, but there are some species and strains that may have negative attributes under certain circumstances. These may potentially produce toxins and act as opportunistic pathogens. One of the primary functions of our favorable bacteria is to help exclude and/or inhibit these pathogenic species from causing harm.

Maintaining a favorable balance of all species of bacteria is key to supporting the health of the microbiome and helping to prevent overgrowth of the potentially pathogenic bacteria strains. An imbalance of bacteria is known as dysbiosis and can lead to symptoms such as bloating, gas, digestive discomfort, diarrhea, and constipation.

What are the best probiotic foods?

Probiotics can be taken as a supplement or through the diet. Foods that are high in probiotics include live yoghurt, sourdough bread, and fermented foods such as kimchi, kefir (milk or water), sauerkraut, and kombucha. Make sure you look for ‘raw’ on the label as any pasteurisation will destroy the bacteria.

Plain live yoghurt	Pickled vegetables	Kefir
Sauerkraut	Apple cider vinegar	Kimchi
Kombucha	Fermented soya (tempeh, miso, natto)	Raw cheese

By consuming a couple of spoonfuls, or half a glass each day, we can help boost the number of friendly bacteria in our gut. If you’re new to fermented foods but would like to give them a try, our advice is to start with just a teaspoon per day and increase the amount slowly over time as introducing them too quickly may result in some side effects, such as bloating and gas.

Supplements can be helpful if you’d rather not include fermented foods in your diet. Look for a research-backed multi-strain friendly bacteria supplement that contains high numbers of commensal bacteria strains that are naturally present in the human gut.

Prebiotics = Food for the probiotics/bacteria

If probiotics are the bacteria themselves, prebiotics are the food that they eat. There are three types – fructooligosaccharides (FOS), galactooligosaccharides (GOS), and inulin. In addition, a type of starch that is resistant to digestion in the upper part of the digestive tract, known as resistant starch, is classed as a prebiotic. 

Derived from plants, FOS are carbohydrates that are indigestible to humans. As a result, they pass through our digestive tract to the large intestine where they act as a food source for probiotics. FOS is derived from plants rather than lactose (see GOS below), making it a suitable prebiotic for anyone with a milk allergy.

GOS is naturally present in breast milk and is thought to help the development of the baby’s microbiome by feeding healthy bacteria, particularly Bifidobacteria and Lactobacilli. GOS can also be derived from lactose in milk. GOS has been shown to have a prebiotic effect even at low levels, which makes it particularly suitable for anyone with IBS, as taking high levels of a prebiotic may cause unwanted bloating.

Inulin is a natural polysaccharide (several simple sugars linked together) occurring in the roots and tubers of certain plants such as chicory.

What does prebiotics do?

Consuming these prebiotics regularly, through foods high in FOS, GOS, or inulin, helps to encourage both the quantity and diversity of our microbiota. 

As well as providing them with fuel, when the beneficial bacteria feed on this prebiotics, they produce by-products, such as short-chain fatty acids (SCFAs), that have been shown to benefit our health. It’s a win-win situation.

What are the best prebiotic foods?

Foods that are high in prebiotic fibre include chicory, garlic, leeks, onions, green bananas, Jerusalem artichokes, and asparagus. 

Resistant starch can be found in cooked and cooled pasta, rice, and potatoes which produces high levels of butyrate, a particular type of SCFA. If these foods don’t form a regular part of your diet, it is also possible to take a supplement containing FOS or GOS to ensure your gut bacteria are well-fed.

Chicory root	Onions	Asparagus
Garlic	Green (unripe) bananas	Legumes
Leeks	Jerusalem artichokes	Cocoa powder

Prebiotic quick facts

• Human milk provides a rich source of prebiotics to the nursing baby. They are known as galactooligosaccharides (GOS) and support infant health by encouraging the growth and colonisation of beneficial microbes in the baby’s gut
• Prebiotic fibres are also found in plant foods such as vegetables, particularly fibrous vegetables such as asparagus and broccoli and the allium group of vegetables that includes onions, garlic, and leeks
• Bananas are a great source of prebiotics – particularly if they are slightly unripe/green
• Beans, legumes, and grains also contain prebiotic fibres. As grains are such a large part of the Western diet, these are the main source for many of us
• By providing food for the microbes, prebiotics may increase the volume of beneficial bacteria present in our gut
• Prebiotics may also help to increase substances produced by bacteria (metabolites) that are important for health
• Prebiotics cannot be digested by humans, it is the live bacteria themselves that gain nourishment from prebiotic food sources, enabling them to flourish
• Did you know that people from prehistoric times consumed prebiotics? Evidence from dry cave deposits shows that humans ate plants high in inulin, a well-known prebiotic fibre present in a wide variety of plant foods

Warning – potential side effects of probiotics and prebiotics

When introducing probiotics into your diet, it can be helpful to start low and build up, particularly if using probiotic foods that contain extremely high numbers of undefined bacteria strains. Using a high-strength supplement can also cause similar effects, although this is less likely as the strains are defined and tested.

The same is also true for prebiotic foods and supplements. As prebiotics are sugary fibers that feed the friendly bacteria and, in some cases, might also feed some of the pathogenic species, they can be more likely to cause a reaction than the probiotic bacteria themselves. The rapid growth in the ‘good’ bacteria that results from them having additional ‘food’, can also lead to them ‘crowding out’ the ‘bad’ bacteria, which can lead to reactions such as gas and bloating.

Any symptoms and side effects should disappear within a few days – if they last longer than two weeks, we recommend reducing the number of probiotics or prebiotics, either on a daily basis or by eating/taking them every other day or every couple of days to start, until your body gets accustomed to the extra bacteria.

In summary

It is important to support the health of your microbiome and this means including

both probiotic and prebiotic foods (or a supplement of either or both) in your diet regularly. Probiotics and prebiotics work together to maintain the health of the gut microbiome.