Probiotics and gut health: what you need to know

Kefir, kimchi, kombucha – supermarket shelves are full of ‘gut-friendly’ 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 to 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.

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What is the gut microbiome?

Your gut microbiota is the unique collection of microbes that live in your gut - these include bacteria, yeast, fungi and viruses and there are trillions of them, most of which live in your colon. 

Your microbiota is responsible for helping you get the most out of your food, ensuring that it’s properly digested and nutrients are absorbed.

But it does more than this. Research into gut health has grown in recent years and the most studied link is the one between the gut and the brain. 

Gut health has been shown to impact your brain and mental health. This explains why we talk about having butterflies in our stomachs when nervous and why people with Irritable Bowel Syndrome (IBS) often have anxiety, and vice versa.

Gut health is also strongly linked to your immune system and it's estimated that 70% of immune cells live in the gut.

What does a healthy gut look like?

Your microbiota is influenced by a range of factors including genetics, diet, environment and age.

Everyone's microbiota is different and individual to only them. While there's no blueprint for what a healthy gut looks like, a diversity of microbes has been linked to better overall health.

People with poor gut diversity feel run down more often and are more susceptible to colds and viruses.

Other symptoms of your gut not functioning at its best include bloating, pain, excessive wind, diarrhoea, constipation and feeling tired or lethargic.

It's normal for most people to experience some of the above occasionally but if symptoms are frequent or constant then it is worth getting it checked out. 

Kaitlin Colucci, a dietitian, told us: 'For some people it's 'normal' to poo up to three times a day. For others it might be three times a week. But if you notice a sustained change in your bowel habits and the consistency of your stools over a prolonged period (around three months) talk to your GP'. 

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Boosting your gut health

As our understanding of the importance of good gut health grows so does interest in boosting your gut health.

The best way to improve your gut health is by eating a varied and healthy diet that contains lots of plant foods. This includes fruit and vegetables but also wholegrains, legumes (chickpeas, beans and lentils), nuts, seeds, herbs and spices. 

Different plant foods contain different nutrients so try to eat a wide range.

Lifestyle factors also impact your gut microbiota so getting enough sleep, managing stress and exercising regularly are important too.

There is some evidence that artificial sweeteners can negatively impact gut health however this research is mainly from animal studies and the links from human studies aren't as consistent.

What is clear is that drinking too much alcohol and smoking are detrimental to gut health, as are some medicines such as antibiotics, proton pump inhibitors (used for acid reflux and stomach ulcers) and laxatives. 

Other medicines, including beta blockers (used to treat blood pressure), statins (cholesterol), and Metformin (type 2 diabetes) appear to have a positive effect on gut health by encouraging the growth of certain gut bacteria.

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Gut health products: the facts

There are plenty of 'gut-friendly' products available in supermarkets, pharmacies and health food shops which contain probiotics or 'friendly bacteria' and promise a range of benefits.

Under current GB and 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, or by adding in other ingredients which do have proven health claims.

From probiotic and prebiotic supplements to cultured products like kombucha and kefir, we've looked at the evidence and talked to experts to bring you a verdict on what's worth trying, and what you can safely swerve.

Probiotics - do supplements work? 

A probiotic is a live organism that has evidence of a health benefit. Because of this the UK and EU consider the term 'probiotic’ to be a health claim. 

As there are currently no approved health claims for probiotics, products containing them can't use this label on their packaging. Instead they're labelled as containing 'live cultures'.

Sophie Medlin, a dietitian specialising in gut health, says: 'There's strong evidence that probiotics do have benefits, but we don't yet have all the answers. Compared to research into vitamins and minerals, the research into probiotics is relatively new. A vitamin supplement will have the same effect on everyone whereas a probiotic won't - it depends on what bacteria is already present in your gut. This is why it's hard to prove probiotics offer the same benefit to everyone'.

Kaitlin Colucci adds: 'For healthy people without symptoms there's no need to take probiotic supplements, but for people with symptoms they can be beneficial'.

When to consider probiotics

There is some evidence that probiotics supplements can help with IBS symptoms and antibiotic-associated diarrhoea. 

But it's not as simple as just picking any product off the shelf. It’s important to match the bacteria strain to your specific symptoms. 

You also need to check there's evidence that proves it reaches your large intestine alive and that the doses used in the study to show a positive effect matches that in the product - studies should be linked on the companies' websites.

The probiotic Saccharomyces boulardii has been shown to reduce antibiotic-associated diarrhoea in some people, whereas Lactobacillus plantarum LP01 and Bifidobacterium breve BR03 have been shown to help some people with constipation.

Experts suggest taking probiotics on an empty stomach.

Probiotic supplements: understanding the label

Probiotic labels can be 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.

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Kimchi, Kombucha and other fermented foods and drinks

Fermented foods include kimchi and sauerkraut which are made from fermented raw cabbage, and kombucha, a sour, fizzy fermented tea. 

The jury is still out on whether these foods and drinks have a beneficial effect on your gut microbiota as the current evidence is limited and there's a lack of good-quality human trials. 

It's hard to carry out good quality trials as the microbes in fermented food are different in every batch, which makes it difficult to standardise and replicate results in studies.

Kaitlin Colucci advises people to 'experiment with fermented foods as they could have a positive effect on gut microbiota'. Sophie Medlin agrees that fermented foods are a good addition to people's diets. She adds: 'While they may not affect your gut microbiota, it doesn't mean they don't nourish your oral microbiome which is also important for health'.

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, for example if they've been pasteurised or fermented in vinegar all the bacteria will have been killed.

Check the packaging to see if it says ‘contains live cultures'.

Kefir, Actimel, Yakult and live yoghurt products

Dairy products naturally contain live bacteria but these are mostly killed during pasteurisation. 

In some cases, live bacteria are added back in post-pasteurisation and in much higher numbers. This is what happens with Actimel, Yakult and Activia yoghurt. 

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.

Kefir is slightly different as it's a fermented milk product that's available as both a yoghurt and drink. It's similar to yoghurt but has a more sour flavour. 

As before, these can't be labelled as probiotics. However you might find that some do have health claims on their packaging, for example 'benefits digestive wellbeing', 'energy support' and 'immune support'. 

But be aware these are based on other nutrients in the product with proven health claims, such as calcium or vitamins B6 and D. 

What does the research show?

As with other fermented foods, the research on kefir and other probiotic dairy has been carried out mostly in labs and on animals rather than humans.  

In the case of kefir, it's hard to measure exactly what concentration of which bacteria each batch contains. But kefir usually contains a broader range of probiotic bacteria than yoghurt-based drinks.

But dietitians Kaitlin Colucci and Sophie Medlin agree that the evidence for the bacteria in kefir and dairy-based probiotics reaching the gut intact is stronger than for kimchi, kombucha and other fermented foods. 

The theory is that the fat in the dairy protects the live bacteria from stomach acid and allows them to travel further down the digestive tract to the colon. 

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Prebiotics - do you need supplements?

Prebiotics are a type of fibre that 'feed' the probiotics in your gut. 

There are many different types of prebiotic and they're found in a wide range of foods including bananas, apricots, figs, grapefruit, onions, garlic, leeks, brussels sprouts, asparagus, artichokes, oats, rye, barley, peas and beans.

As they're so widely available, by eating a diet with a variety of plant foods you shouldn't really need to take prebiotics in supplement form.  

It can sometimes be tempting to 'top-up' with a supplement but a high-dose of prebiotics can be problematic and trigger unwanted symptoms such as bloating and diarrhoea in around 15-20% of people, especially those with IBS.

Sophie Medlin warns: 'Probiotic supplements often contain prebiotics too and some people find instead of helping their symptoms, they make them worse'. 

She adds: 'Chicory inulin (a prebiotic) is naturally sweet so manufacturers often add it to cereals, cereal bars and other foods. It increases the sweetness of the final product without them having to add sugar and it's the only prebiotic that has an authorised health claim - to aid normal bowel function - so they have the added benefit of being able to add this to their labelling'.

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The golden rules of gut health

1. It's about more than your diet

While dietary diversity is important, your gut health also depends on other factors such as minimising stress, getting enough sleep, exercising, limiting alcohol content and not smoking. 

If you have gut issues, it's worth limiting your intake of caffeine and fried or spicy food. 

2. Don't go it alone

If you have ongoing or new issues, it's better to discuss these with your GP rather than trying to solve it alone.

While it can be tempting to add a probiotic supplement into your diet, they can sometimes make symptoms worse.

3. Don't expect overnight transformations

It's best to make any changes to your diet gradually. 

This is especially true in the case of increasing your fibre intake, or adding probiotics or fermented foods. 

You need to give your gut time to adjust to the changes and adding too much too soon could exacerbate symptoms such as bloating. Try adding a half of a portion of a probiotic or fermented food each day for a week before increasing the amounts.

It's also important to increase your water intake when you increase your fibre intake.

4. Avoid cutting out whole food groups

Dairy and gluten are often blamed when people have IBS or are suffering with gut problems. 

But cutting them out is not without risks.

A restricted diet of any sort starves us of a diverse range of prebiotics and probiotics as well as risking nutritional deficiencies.

Cutting out all dairy can make it hard to get enough calcium and by removing all foods containing gluten it could be harder to get enough fibre.

It's best to seek guidance from a dietitian on any exclusions. Kaitlin Colucci says: 'Gut health is about inclusion not exclusion'.

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