The terms prebiotics and probiotics are used frequently in the mainstream media nowadays. In this blog we look at what they are, what foods they are contained in, and why you might want to eat them. Before we start, we first need a common understanding of the gut microbiome.

The gut microbiome

A microbiome is a community of micro-organisms – including bacteria, fungi, yeasts and viruses – that live in the body. Humans have several different microbiomes, such as those in the mouth and on the skin, but the largest is found in our large intestine and is called the gut microbiome.

The gut microbiome contains a staggering 39 trillion bacterial cells. It might make you feel a little uneasy when you first contemplate having so many “bugs” inside you, however, humans and our gut microbes have evolved together, and each provides benefits for the other. The human gut provides food and a warm environment for microbes, and they in turn provide health benefits to us. Some of these include:

  • Supporting digestion
  • Alerting our immune system to the presence of potential pathogens in the digestive tract, and directly killing some of these themselves
  • Regulating our immune system so that it reacts appropriately to threats (ie it neither ignores them nor overreacts)
  • Maintaining a healthy gut lining
  • Synthesising certain nutrients, such as B vitamins and vitamin K

The gut microbiome also has profound and wide-reaching effects on areas of our health that might not at first seem to be linked to it. We know of associations between the gut microbiome and mental health, joint health, hormone balance and even skin conditions, to name just a few.

The importance of diversity

Research has revealed that the healthiest people tended to have the most diverse gut microbiomes. This means that we want to encourage a wide variety of microbial species to thrive in our guts, rather than just a few overgrown species dominating.

There are two separate classes of food compounds that together shape our gut microbiome: prebiotics and probiotics.

Prebiotics are elements of foods, particularly fibres, that we humans cannot digest, but which promote the growth of beneficial microbes in our gut. In other words, they are foods for our gut bugs.

We know that fibre is important for our digestive health and for bowel regularity, but there’s more to it than that. After we have absorbed nutrients from our food in the small intestine, fibre continues its journey into the large intestine. Here it can be used as an energy source for certain beneficial bacteria. Eating a diet high in prebiotic fibres thus encourages the growth of beneficial bacteria.

Research has shown that by increasing numbers of beneficial bacteria in the gut, prebiotics have a favourable effect on the immune system. They also increase the absorption of minerals from the diet, may reduce LDL cholesterol, protect against gastrointestinal infections, and reduce the risk of colorectal cancer.

The beneficial bacteria also undertake a kind of crowd control in the gut, and when we have a healthy amount of them they leave no space for unwanted, or pathogenic bacteria to take hold.

Additionally, the good bacteria produce compounds called short chain fatty acids, which have an anti-inflammatory effect within the colon.

Remember that we want to have high diversity within our microbiome? Different bacterial species thrive on different fibres, so eating as wide as possible a range of high fibre plant foods is one of the best ways to encourage diversity.

Whilst all plant foods contain some prebiotic fibres (although not juices, where the fibre has been removed), the following foods are particularly high in prebiotic fibre:

  • Oats
  • Leeks, onions and garlic
  • Pulses: beans, lentils and chickpeas
  • Asparagus
  • Jerusalem artichokes
  • Apples, particularly when they brown slightly, such as when grated or stewed
  • Seaweed

Making sure that you eat some of these foods daily is a very good way of encouraging good gut bacteria. However, if you do not currently eat a lot of prebiotic fibre, then it is best to start with small amounts and increase gradually. When bacteria ferment the fibre they produce gas, and this can cause discomfort until your gut becomes accustomed to it. If you find that your gut doesn’t tolerate a certain prebiotic food, try another.

The term “probiotics” refers to the live microbes themselves that benefit our health. There are many different strains of probiotics, and the health impacts depend on the particular strain. You may be aware of probiotics supplements, but these beneficial organisms are also found in fermented foods.

Fermented foods
Humans have been fermenting foods for centuries, probably as a way of preserving food in the days before refrigerators. As foods ferment, beneficial microbes (which are either naturally present in the food or are added as a “starter” culture) multiply. Many of these bacteria produce lactic acid, and these particular bacteria give fermented foods their notable tangy taste as well as many of their health benefits. Fermented foods tend to contain more different species than probiotic supplements do.

Given that the gut microbiome affects our body far beyond our digestive system, it should not be a surprise that fermented foods are associated with multiple health benefits. They help support digestion, may reduce symptoms of IBS, can improve blood sugar control and support good mental health and cognitive function. Fermented milk products such as kefir and yoghurt can help increase lactose tolerance in people who are normally intolerant. Fermenting vegetables such as cabbage helps to make the nutrients they contain more available to the body.

Some of the most consumed and most readily available fermented foods are “the 4 Ks”: kefir (a fermented milk drink), kombucha (fermented green tea), kimchi (a Korean fermented vegetable dish) and kraut (sauerkraut, fermented cabbage). It is cheap and relatively easy to make your own fermented foods at home. However, if you have never eaten fermented foods you might prefer to buy some to try at first, and they are now readily available in large supermarkets as well as in health food shops. When buying sauerkraut or kimchi, make sure to choose a non-pasteurised and fermented version; it should not contain vinegar. Click here for an easy sauerkraut recipe.

It is best to eat fermented foods daily to benefit from them. A small amount is enough to start with; little and often is better than a large amount once a week.

In conclusion, both prebiotic and probiotic foods have distinct benefits, not just for our digestive system but for our health overall. An 2021 study found that while diets high in prebiotic fibres changed the microbiome and influenced the immune system, eating fermented foods was a better way to improve microbiome diversity. The ideal is to have a mix of both, so why not try including one or more prebiotic-rich foods and a small amount of fermented foods daily?

For more information on digestive health, why not book our seminar/webinar Good Health Starts in the Gut. Call 07966 478974 for more details.

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