Probiotics, Prebiotics and Postbiotics: Which Is Best For Health And Longevity?

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There’s growing evidence that the microbes in our guts are major players in health and disease, which has led to a rise in popularity of supplements designed to support a healthy gut microbiome. These are classified as pro-, pre- and postbiotics. In this article, we’re going to break down the pros and cons of each and cover some points that supplement providers won’t usually tell you.

Why We Should Care About Gut Microbes

The average human gut contains hundreds of different species of bacteria, with the exact number varying depending on measurement methods. Either way, that’s a lot of biodiversity to exist within a single organ system. But why should we care about these hangers-on? Bacteria in our guts feast on fibre, a component of food that we struggle to break down. In doing so, they produce molecules that can affect the nearby gut and resident immune cells, which can have wide ranging effects on even distant organs including the central nervous system. Some studies have even shown that gut bacteria can influence what foods we crave! What’s more, gut bacteria protect us against infectious diseases by outcompeting pathogenic bacteria that invade the gut.

Studies suggest that having more different species of bacteria living within the gut, as well as having more of certain species, correlates with improved overall health. Microbiome diversity tends to decrease with age, and some studies suggest that restoring this diversity can slow ageing to some extent. Since different bacteria prefer different foods, a diverse and healthy diet tends to foster a diverse microbiome, which in turn has a powerful effect on overall health. There are however more targeted ways you might be able to improve the health of your gut, and this is where pro, pre, and postbiotic foods and supplements come in.

Probiotics

Good dietary sources: certain fermented foods (yoghurt, kefir, sauerkraut, some cheeses…)

What are they?

Probiotics are live microorganisms that are found in certain foods and supplements. They contain those bacterial species that we believe to have beneficial effects within the gut, based on findings that show that their presence correlates with good health. These beneficial bacteria can become depleted and outcompeted by ‘bad’ gut bacteria due to factors like poor diet and advancing age. Probiotics can (temporarily – see below) replenish good bacterial species and address imbalances in the microbiome. 

Strengths and weaknesses

Scientific research is generally favourable towards probiotics, suggesting that they can be useful in the treatment of some diseases while further improving health in already healthy people. However, the level of hype around probiotic supplements often exceeds what would be justified by scientific research, with many studies cautioning that more research should be conducted. 

Because of the complex interactions between diet and the hundreds of different bacterial species within each individual’s gut, a probiotic that is beneficial for one person might be ineffective or even harmful to someone else. This has led to some inconsistent effects for probiotic supplements in clinical trials, such as this study in which some patients saw significantly improved blood sugar when taking probiotics, while other participants’ blood sugar significantly worsened.

There’s also a chance that probiotics could outcompete some native gut bacteria. The gut is often described as containing ‘good’ and ‘bad’ bacteria, but in reality even bacterial species that are considered ‘good’ can become bad if they crowd out other good bacteria, and there is some concern that indiscriminate use of probiotic supplements could lead to such a situation. These concerns do not generally apply to fermented foods because these contain a more diverse but less concentrated population of bacteria.

Finally, many people may not realise that commercial probiotic supplements are not naturally present within humans, which means that they cannot actually survive in our guts indefinitely. This means that if you stop taking probiotics, any benefits you were getting will wear off quite quickly.

Prebiotics

Good dietary sources: garlic, leeks, cocoa, whole grains and other fibre-rich foods

What are they?

Unlike probiotics, prebiotics contain no live microorganisms. Instead, they are non-digestible fibres that feed the bacterial species in the gut that are thought to be beneficial. While probiotics add bacteria to the gut, prebiotics help support the good bacteria already present. 

Strengths and Weaknesses

Like probiotics, the evidence concerning the effects of prebiotics on human health is generally favourable, with some inconsistencies and more research needed to fully understand who benefits the most from different prebiotics. The main advantage of prebiotics is that they are not introducing foreign bacteria into the gut, but instead supporting the native bacteria that are already there, and sometimes inhibiting the overgrowth of disease-causing bacteria. This is likely to make them a safer and more reliable alternative to probiotics – when it comes to medicine, it’s usually better to prevent a health problem than to treat it after it has occurred.

Of course, prebiotics are not able to restore a species of bacteria that has been lost from the gut. Currently, the only way of permanently restoring a species once it has been lost is by faecal transplantation from someone with a healthy microbiome. Furthermore, just like in the case of probiotics, the benefits of prebiotics may vary greatly from one person to another, since their effects depend on existing gut health.

Postbiotics

Good dietary sources: any probiotic-containing food

What are they?

Postbiotics are a more recent concept. They are essentially dead probiotics in various stages of breakdown. They can include whole, intact bacteria that are dead, or just the individual components that made them (enzymes, fatty acids, cell walls and so on). Most importantly, postbiotics come with the beneficial molecules the bacteria were producing when they were alive. This means that any dietary probiotic will naturally contain postbiotics as well, due to the natural deaths of fermenting bacteria. If we think of gut bacteria as the factories and prebiotics as the input materials, postbiotics are a way of skipping straight to the output materials without having to worry so much about the complex interactions between diet and live microbes living in the gut.

Strengths and weaknesses

Postbiotics should in theory deliver many of the same benefits as probiotics, but since they contain no live bacteria, they should not be capable of causing significant harm to the gut’s native microbiome. However, the amount of research studying them is small in comparison to probiotics and prebiotics. While there’s some promising data, it’s too early to conclude that postbiotics are the best way to shore up your gut microbiome.

The Take-Home Message

The healthiest way to support gut health is to consume a diverse diet containing fermented foods rich in probiotics and postbiotics, alongside foods rich in fibre. This ensures you get the beneficial bacteria alongside the prebiotics they need to produce beneficial metabolites, not to mention the fact that most of these foods contain many other beneficial compounds. Ultra-processed foods are best avoided, as these have usually had most of their fibre stripped from them during manufacturing.

If you have difficulty making these dietary modifications, the research doesn’t yet have a clear answer as to which ‘biotic’ supplement is the most beneficial, but prebiotics and postbiotics may be more predictable and consistent, while probiotic supplements may have the potential to do more harm than good in some circumstances.