top of page

The Good, the Bad, and the Bacteria: Understanding the Importance of Probiotics and Prebiotics

There’s so much information out there on gut health now and in particular on our gut microbes. You may have 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.

Probiotic supplementation is a huge business and I often see many people taking lots of them for long periods of time, often unnecessarily. They are certainly warranted in some cases but certainly not all and probiotic supplements often don’t address many common digestive conditions or complaints.

Having said that I want to talk a little about our microbiome and explore the types of foods that can really support a robust and diverse microbiome which will do wonders for your digestive and overall health.

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.

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 you can have a situation called ‘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.

Image of woman at laptop sneezing into tissue
The gut microbiota has a symbiotic relationship with the immune system

5 important things your gut bacteria do for you

  1. Kill bugs and hostile bacteria Gut bacteria helps eliminate harmful bugs and bacteria, including those responsible for food poisoning or stomach ulcers, which can lead to unpleasant symptoms or diseases.

  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 – helping to keep you regular.

  4. Make vitamins & improve the absorption of nutrients Your gut bacteria are responsible for making many B vitamins, and these same bacteria help you better absorb the minerals in the food.

  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.

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 about the microbiome and its role in health, and in developing strategies to maintain or modify the microbiome for therapeutic purposes.

As a nutritional therapist I do quite a lot of stool testing with my clients (well, I work with labs that do the tests, I do the interpretationJ). 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 vagina!

Graphic of large intestine surrounded by bacteria
Digestive issues can be an indication of an imbalance in the gut microbiome

One of the ways you can keep a healthy gut environment is to address any digestive problems you might be struggling with (we work with all manner of digestive conditions so do get in touch if you need help in this area).

We also need to eat the kinds of foods our gut really needs and (potentially) take supplements to help ensure that the bacterial balance in your gut microbiome stays positive in spite of the impact a Western diet, stress, medications and so on can have. 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: 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: 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: 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: 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.

Organic red misto paste
Miso is rich in probiotics, antioxidants, and vitamins

Miso: 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. More often than not, these either have added sugars or sweeteners to make them palatable. My preferred choice is unsweetened kefir over these types of drinks.

About prebiotics

Prebiotic foods such as leeks, garlic and onions
Onions, garlic and leeks contain prebiotics fibres such as FOS and GOS

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.

Colourful ruciferous vegetables including bok choy, kale, broccoli, cauliflower
Consuming cruciferous vegetables can support gut health by providing prebiotics

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 and kale.

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). You may have heard to the term SIBO (Small Intestinal Bacterial Overgrowth). 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 me 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 GOS or PHGG 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.

Maintaining a robust and thriving gut microbiome is of utmost importance for overall health and well-being. The impact of our dietary choices on the gut microbiome cannot be understated, particularly in the context of the Western diet, which has been shown to adversely affect the diversity of this microbial ecosystem.

By embracing a diet that prioritises both probiotic and prebiotic foods, we can actively support the flourishing of a diverse and resilient gut microbiome. This dietary approach not only enhances gut health but also contributes to our overall well-being by optimizing digestion, bolstering immune function, and mitigating the risk of various diseases.

If you would like support in improving your gut health and overall well-being, then please get in touch and book your free health check today.

Recent Posts

See All


bottom of page