Probiotics and gut health: what you should know

Kefir, kimchi, kombucha – supermarket shelves are filling with so-called ‘gut-friendly’ probiotic products. But can they really transform your health, or are you just flushing money down the drain?

Probiotic foods and supplements can be pricey, and it's hard to cut through the clever marketing and know what's worth buying, and what's best left on the shelf.

We’ve consulted leading gut health experts to untangle what the evidence says about common gut health products, and what simple steps you can take to look after your gut health.

What is the gut microbiome?

The gut microbiome is a vast ecosystem of complex organisms that live in our digestive tract. It’s responsible for helping us get the most out of our food, ensuring that it’s properly digested and nutrients are absorbed.

It’s also home to 70% of our immune system, as well as trillions of microbes that have an effect on our health more generally, including mental health, heart health, kidney health and more besides.

Probiotic ‘good bacteria’ occur naturally in your gut and play a crucial role in this microscopic world. However, they can be disrupted by a range of factors, including poor diet, stress or taking a course of antibiotics.

Probiotic foods and supplements contain similar bacteria that are meant to be beneficial to your gut microbiome, while prebiotics supply essential nutrients that stimulate the growth of the ‘good bacteria’ that already exist in your gut.

Boosting your gut health

As our understanding of how important good gut health is for our wider health, interest in boosting your gut health has grown.

But when it comes to how exactly to support our gut microbiome, things can get complicated. Nobody really knows what a 'normal' microbiome should look like and the diversity of gut bacteria varies from person to person.

While the best way to boost your gut health is by eating a varied and healthy diet, getting enough sleep, and managing stress, there is some evidence for probiotics being beneficial, depending on what your symptoms are. And there is emerging evidence for other products too.

If you have ongoing, difficult-to-treat gut complaints, such as constipation, diarrhoea or bloating, you should keep track of your symptoms in a diary and then see your GP, who may refer you to a dietitian.

The golden rule is to tailor treatment to your specific symptoms. For example, certain strains of probiotics have some evidence of reducing IBS symptoms, but others don’t.

Some treatments might actively make things worse – for example, large doses of prebiotics could trigger IBS symptoms.

Gut health products: the facts

Under EU regulations, food and drink products aren’t allowed to claim to treat or cure a health issue. Many manufacturers get around this by using vague marketing buzzwords which don’t have any objective scientific meaning.

There are more than 250 non-authorised claims for probiotic products on the EU Register for nutrition and health claims, a few common ones include:

• Bio-live
• Supporting the immune system
• Promoting gut health
• Gut-friendly/gut-loving/beneficial bacteria

Read on to find out about the different ‘gut friendly’ products you’ll encounter – from probiotic and prebiotic supplements to cultured products like kombucha and kefir. We've examined the evidence for each, and explain what to look out for before giving them a go.

Pro and prebiotic supplements

Do probiotics work?

There’s no overall consensus about the effectiveness of taking probiotic supplements.

The word ‘probiotic’ is not allowed to appear on products sold within the EU as no health claims have been accepted as proven when the evidence has been assessed by the European Food Safety Authority (EFSA). 

Some probiotic species, such as lactobacilli and bifidobacteria, are thought to produce compounds called short-chain fatty acids, which stimulate the growth of good bacteria already in the gut and provide energy to the gut wall.

When to consider probiotics

While more research is needed for the EFSA to approve any health claims linked to probiotics, there is some evidence that probiotics can help with IBS symptoms and antibiotic-associated diarrhoea, but it’s important to match the bacteria strain to your specific symptoms.

Some strains that have been studied in human clinical trials include:

• Lactobacillus rhamnosus GG has some evidence to help prevent antibiotic-associated diarrhoea.
• Bifidobacterium lactis has been linked in some studies to constipation relief.
• There is some evidence for probiotics helping IBS, but it may not work for everyone. Some products that have published studies in relation to IBS include Alflorex, BioKult Advanced, Symprove and VSL3. 

Experts suggest taking probiotics on an empty stomach and as a liquid formulation instead of solid, where possible, as the bacteria in liquid probiotics don’t have to rehydrate in the gut, so may be more effective.

Probiotic supplements: understanding the label

Probiotic labels can be really difficult to decode if you don’t know what you’re looking at. If you’re browsing probiotics in store, check for two main things:

• Strain of bacteria: This is the first thing you should check. Before you take it, check whether it has been tested in a human clinical trial. You can look up bacterial strains and the corresponding evidence on usprobioticguide.com.
• Number of bacteria: The range in billions of bacteria between different probiotic supplements can seem baffling – from 100 million to more than a trillion. More isn't necessarily better - it depends instead on the dose that has shown demonstrable results in humans.

Kombucha, Kimchi and other fermented foods

Fermented drinks, such as kombucha (a slightly sour, fizzy flavoured drink made from sweetened tea and bacterial cultures) and foods such as miso, kimchi and sauerkraut, are associated with positive digestive health, but the evidence for this is somewhat limited.

A lack of evidence doesn't necessarily mean these foods aren’t beneficial, but not enough studies have been done to prove their effects. The microbes in fermented food are different in every batch, which makes it difficult to standardise and replicate results in studies.

Should you be eating fermented food?

Fermented products can contain a wide variety of bacteria and minerals that contribute to gut diversity. It's hard to know what bacteria is in these foods and what bacteria your body needs, so it’s worth experimenting by including a range of them in your diet (gradually, not all at once!).

Be aware that fermented foods such as kimchi and miso can be high in salt, and not all fermented food contains live bacteria. Check the label for ‘contains live cultures.’

Actimel, Yakult and other live yoghurt drinks

Probiotic yoghurt drinks such as Actimel and Yakult, along with live yoghurt, have been supermarket staples for many years and, as such, have a little more research behind them than some of the more recent fermented food options.

Activia has been shown to help relieve constipation, and there are some studies linking Actimel with the prevention of antibiotic-associated diarrhoea. However, in both cases the evidence has not been deemed strong enough to be authorised by the EU register on nutrition and health claims.

Some products only have one strain of bacteria in them, which limits their efficacy beyond milder symptoms. Most will have more, but check the label.

What about Kefir yoghurt drinks?

As with other fermented foods, kefir – a traditional Eastern fermented milk product available as both a drink and yoghurt – also has limited clinical evidence behind it. It's hard to measure exactly what concentration of which bacteria each batch contains.

Kefir products usually contain a broader range of probiotic bacteria than yoghurt-based drinks, though.

As a milk-based product, it can be high in sugar (bearing in mind 250ml of plain milk has 12g of naturally occurring sugar as lactose).

Foods that boost your gut health naturally

Ideally, you should aim to include a range of prebiotic, probiotic and fibrous foods in your diet. This is likely to be cheaper than relying on supplements too.

As the image below shows, prebiotic foods include apples, bananas, onion, asparagus and leeks, while easy sources of probiotics are yoghurt and fermented foods.

Variety is key, but make sure you introduce food that you are unfamiliar with gradually to avoid any side effects.

Don’t forget the fibre either: it’s not as trendy as some of the newer gut health products, but most of us could do with adding more fibre to our diet. Good sources are fruit and veg, beans and pulses, and whole grains.

There is strong evidence that eating lots of fibre lowers the risk of heart disease, stroke, type 2 diabetes, bowel cancer and more.

It also helps you feel fuller for longer, and can aid digestion and in preventing constipation. Many fibrous foods are also prebiotic, making these choices a win-win for digestive health

Thanks to Dr Simon Gaisford, Dr Samantha Gill, Dr Megan Rossi and Priya Tew for their contributions to this article.