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Probiotics and prebiotics. What are they and why are they important?

You’ve probably heard people talk about ‘good’ and ‘bad’ bacteria and that we want to have more ‘good’ bacteria because this has a positive effect on your health. I’ll bet you may also have a conceptual idea that probiotics will help you, and perhaps you’ve seen little bottles of probiotics advertised as the saviour of your health. Today I want to let you know why this all matters, so that you can make the best choices for your health.

bacteria water colour painting

Good v bad bacteria

When we talk about bacteria in the gut, we are usually talking about bacteria in the large intestine, the colon. Your ‘microbiome’. The microbiome is a parallel universe of all kinds of different microorganisms running all through your digestive tract, that runs from your mouth to… well, the other end.

Most of these organisms are bacteria, and there are lots more of these than there are cells in your body - about ten times as many. The balance of the bacteria in your digestive system has implications for your health in general and not just your innards. In short, it’s important to have the right kinds of bacteria in the right places. It matters that the ratio of good to bad bacteria works – when you’re out of balance (when there are more unfavourable bacteria and other microorganisms) nutritionists call this ‘dysbiosis’.

These microorganisms play a crucial role in maintaining overall health, as they help to break down food, make vitamins, regulate your immune system, and prevent the growth of harmful pathogens. When we think about the gut, consider we want a balance between the good and bad microorganisms, a victory of ‘good’ over ‘bad’ bacteria and yeasts, and so on.

Research tells us the composition of the microbiome can vary widely from person to person, and that changes in the microbiome may be associated with a variety of health conditions, including inflammatory bowel disease, obesity, and diabetes.

As a result, there is growing interest in understanding more the microbiome and its role in health, and in developing strategies to maintain or modify the microbiome for therapeutic purposes. As a nutrition practitioner, it’s one of the areas that fascinate me and I spend a lot of time in clinic talking to people about how they can use food and supplements to support the health of their microbiome.

(As an aside, although the word microbiome is most commonly associated with the gut, in reality, your microbiome also refers to other parts of the body, such as the skin, mouth, and reproductive tract.)


One of the ways you can keep a healthy gut environment is to tackle any digestive problems you might be struggling with (ask me if you need help), eat the kinds of foods our body really needs and (potentially) take supplements to help ensure the bacterial balance in your gut microbiome stays positive in spite of what 21st century living may throw at it. Eating probiotic foods and prebiotic foods can help.

Probiotic foods

Probiotic foods are foods that naturally contain live microorganisms like bacteria or yeasts. They are often referred to as "functional foods" as they provide nutritional benefits beyond basic nutritional needs. Think of these as providing your body with additional healthful bacteria.

Some of the most common probiotic foods include:

yoghurt drink with pommegranit


Yoghurt is made by fermenting milk with bacterial cultures, typically Lactobacillus bulgaricus and Streptococcus thermophilus. Some yogurt products also contain additional probiotic strains, such as Lactobacillus acidophilus and Bifidobacterium lactis.


Kefir is a fermented milk drink that is made by combining milk with kefir grains, which contain a mixture of bacteria and yeasts. Kefir is rich in probiotics and may also contain other beneficial compounds, such as vitamins and minerals.


Sauerkraut is a fermented cabbage dish popular in Europe that is made by combining shredded cabbage with salt and allowing it to ferment for several days. The fermentation process produces lactic acid, which gives sauerkraut its distinctive sour taste and also serves as a natural preservative.


Kimchi is a spicy Korean dish that is made by fermenting vegetables, typically cabbage, with a mixture of spices and seasonings. Kimchi is rich in probiotics and may also contain other beneficial compounds, such as antioxidants and anti-inflammatory compounds.


Miso is a Japanese condiment that is made by fermenting soybeans with a type of fungus called Aspergillus oryzae. Miso is typically used as a seasoning in soups and other dishes and is rich in probiotics and other beneficial compounds, such as antioxidants and vitamins. You can buy miso soup to drink as a snack and also miso paste, which you might use in cooking, from many supermarkets.


What about probiotic drinks?

You will undoubtedly seen mass-produced and heavily advertised drinks like Actimel and Yakult on supermarket shelves. Unfortunately, many of the popular ones do not have enough bacteria and/or the bacteria do not survive the harsh digestive environment in the gut, therefore do not have an impact. Just swallowing something ‘good’ is not enough. These additionally either have added sugars or sweeteners to make them palatable.

Probiotic supplements

You’ve likely also have seen probiotic supplements, even on supermarket shelves and wondered whether you should take one.

A supplement cannot replace a good diet, but it can help provide targeted support. If you have digestive problems, let’s have a chat about what we can do to help. Since everyone is different and we all have a unique microbiome, truly targeted support can look like finding specific strains of bacteria to support certain conditions (some strains are great for supporting low mood, others are helpful for hormone balance, and so it goes on). These are often not the kinds of products that should be taken without professional recommendation.

That said some of the key beneficial bacteria that can help include lactobacillus (acidophilus and rhamnosus) and the bifidobacteria group (breve, longum, lactis). Bottom line, what will most benefit you very much depends on the specific symptoms or conditions you are dealing with.

About prebiotics

Prebiotics are a type of dietary fibre that are not digested in the small intestine, but instead reaches the large intestine where they serve as a food source for beneficial gut bacteria. So, while probiotics provide additional bacteria, prebiotics feed the bacteria that are already there and help promote the growth and activity of specific types of bacteria that are considered beneficial for health.  

Some common types of prebiotics include inulin, fructooligosaccharides (FOS), and galactooligosaccharides (GOS). These prebiotic fibres are found naturally in many plant-based foods, such as bananas, onions, garlic, leeks, asparagus, artichokes, and whole grains.


Cruciferous veggies are also very helpful for your digestion, you should know that they contain compounds called glucosinolates, which are fermented by bacteria and used as fuel. They are also prebiotic.

Examples are: Bok choy, broccoli, Brussels sprouts, cabbage, cauliflower, kale and spring greens.

Prebiotics have been shown to have a variety of health benefits, including improving digestion, boosting the immune system, reducing inflammation, and improving the absorption of certain nutrients. Additionally, research suggests that prebiotics may help reduce the risk of certain health conditions, such as type 2 diabetes, heart disease, and colorectal cancer.

It is important to note that while prebiotics are beneficial for health, they can also cause digestive discomfort in some people, particularly when consumed in high amounts. Anyone with IBS, for example, should approach some of these foods with care.

What lurks behind the majority of cases of IBS is bacteria in the small intestine, where we don’t really want it (large intestine, yes, small intestine, no). Your body really should do a daily swoosh of all bacteria from the small intestine down to the colon (called the Migrating Motor Complex) but for a variety of reasons that might not occur.

What can then happen is the bacteria in the small intestine can feast on these lovely prebiotic foods, causing gas, bloating and discomfort. That’s not my telling you don’t eat these foods but, if you have digestive problems, start with small quantities until you work out what your body can tolerate.

You can also buy prebiotic supplements like FOS but I wouldn’t advise these unless you are working with a nutrition professional. They can be really helpful in a digestive health programme but only if you know what you are doing and which specific products to buy.


A healthy microbiome


5 important things your gut bacteria do for you

1. Kill bugs and hostile bacteria

these can cause unpleasant symptoms or disease – like the ones that cause food poisoning or stomach ulcers.

2. Boost your immunity

60% of your immunity is in your gut and the immune tissue in your digestive system is very sensitive to bacterial activity. The good bacteria also encourage the body to make a particular kind of antibody that stops you getting sick.

3. Improve digestion

Some bacteria help you break down particular foods and even help with the muscular contractions that move food through your system – thus keeping you regular.

4. Make vitamins & help you absorb nutrients better

Your gut bacteria are responsible for making many B vitamins, and these same bacteria help you absorb minerals in the food you eat better.

5. Protect against disease

Some bacteria produce enzymes that turn the fibre you eat into short chain fatty acids (SCFA). This is interesting because these SCFAs can help protect against heart diseases by regulating cholesterol and having a positive impact on fats in the blood. A particular type of SCFA called butyrate has been shown to be protective against cancer.

If you’ve been struggling with tummy problems for a while or want to discuss any other health concerns. Why not book a free 30-minute mini-consultation with me here?

We can talk about what’s bothering you and I can give you some tips to get you heading in the right direction.


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