Probiotic foods and supplements like Yakult "contain specific strains of bacteria with proven health benefits". Photo / Getty Images
Experts explain how our skin, immune system and mental health can all improve if we improve the balance of bacteria in our digestive system.
From improved immunity and mental health, to weight loss and smoother skin, the supposed benefits of probiotics are endless, and in particular when it comes to improving your gut health.
Probiotics are live bacteria and yeasts, often described as “good” or “friendly” or “bad”. The balance of good and bad bacteria in your gut can be affected by several factors such as stress, antibiotics and a poor diet, and probiotics can tip the balance back in the favour of good bacteria.
Little wonder that the global probiotic market, which includes supplements, yogurts and powders, is expected to reach $105.7 billion by 2029 (up from $71.2b in 2024).
But what’s the scientific evidence of the health benefits, and how much of a difference do they really make?
“First of all we need to make a distinction between probiotics and fermented foods,” says Sam Rice, the Telegraph’s nutritionist and author of Supercharge Your Diet: Ten Easy Ways to Get Everything You Need From Your Food.
“Probiotics are specially developed foods or supplements that contain specific strains of bacteria with proven health benefits, for example, Yakult milk drinks which contain L. casei Shirota, which studies show help with constipation. Fermented foods, such as miso or kefir, meanwhile, contain a wide range of live bacteria which increases gut bacteria diversity, improving overall gut health.”
Dr Federica Amati, the head nutritionist at Zoe and the author of Every Body Should Know This, says the evidence that probiotic supplements can support gut health varies for different strains: “The evidence is better for consuming probiotic foods, like natural yogurt, kimchi and other fermented products as well as for a plant-rich diet. Fermented plants, such as kimchi [fermented mixed vegetables] provide a double-whammy – they contain probiotic bacteria alongside prebiotic fibres that act as a fertiliser for your gut microbiome”.
“Although scientists are still investigating, it does seem that probiotic foods might support a healthy immune system,” says Amati.
“Probiotics contain species of ‘good’ bacteria’. When these bacteria reach your gut, some of them become active as part of your gut microbiome [ie the trillions of microbes such as bacteria, fungi and viruses that live predominantly in our gut and affect our digestion, along with our immune system and mood], increasing the number and diversity of the species in your gut microbiome.
“A surprising 70 per cent of your immune cells live just outside your gut. Introducing new strains [of bacteria] and encouraging a diverse and beneficial gut microbiome population helps ‘train’ your immune system and supports good immune response as well as reducing excess inflammation.”
During a small study in 2021, researchers at the Stanford School of Medicine in the United States found that consuming fermented foods can enhance gut diversity and may benefit the immune system. Those who ate fermented foods such as kefir, kimchi, kombucha tea and other fermented vegetables had an increase in their overall gut diversity. “Microbiota-targeted diets change immune status, providing a promising avenue for decreasing inflammation in healthy adults,” said Professor Christopher Gardner, the director of nutrition studies at the Stanford Prevention Research Centre, who worked on the study. “This finding was consistent across all participants in the study who were assigned to the higher fermented food group.”
“We know that good gut health has an effect on mood via the gut-brain axis, and there is research to show that better gut health can help alleviate symptoms of depression, for example,” Rice explains.
A 2019 study published in the journal Nature Microbiology even questioned whether probiotic treatments could be used for depression. Belgian researchers found that higher levels of two types of gut bacteria – faecalibacterium and coprococcus – were associated with better mental health thanks to their anti-inflammatory properties. “If depressed people are really missing these bacteria, the future outlook is developing these as so-called psychobiotics,” said Jeroen Raes, the study’s co-author.
And it seems the gut-brain connection works the other way too. A 2024 study from King’s College London found that treatments used for depression, anxiety and stress significantly reduced inflammation in the digestive tract and could even treat conditions like inflammatory bowel disease (IBD), an autoimmune disease that comprises Crohn’s disease and ulcerative colitis. “Our study showed that interventions that treat mental health reduce levels of inflammation in the body,” reports Natasha Seaton, one of the study’s authors. “This indicates that mood interventions could be a valuable tool in our approach to help those with IBD.”
“As probiotic supplements only contain specific strains of bacteria it’s unlikely they will help with specific health goals like weight loss,” says Rice. However, Rice says that by eating a range of fermented foods we can improve our overall gut health, which we know does help with weight loss. “This is because your appetite regulation is better and your digestion is more efficient when gut health is improved.”
“The health of our gut is linked to the health of our entire body, so if you have a healthy gut microbiome, you’re more likely – but not guaranteed – to have healthier skin,” says Amati. “However, looking at links between these systems is incredibly challenging because there are trillions of bacteria living in our gut and on our skin, all of which produce a cocktail of compounds that have a wide range of effects. However, scientists have found some links between gut health and skin health via the so-called gut-skin axis. There is stronger evidence for improving dietary quality with a Mediterranean diet for example, and improving both of these outcomes.”
The gut-skin axis refers to the link between our skin and gut health. For example, certain conditions such as inflammatory bowel disease and coeliac disease are associated with skin conditions such as eczema, psoriasis, dermatitis and rosacea. A study published this year in the International Journal of Molecular Sciences examined the use of probiotics in treating various skin conditions, with the researchers finding that improving gut health had an impact on the severity of skin conditions.
There are several different strains of probiotics and they each offer different benefits. Broadly speaking there are two main types – Bifidobacteria and Lactobacillus – with various subcategories within them. They’re often abbreviated to B. and L. and then combined with a subcategory. For example, B. animalis, found in probiotic yogurts that claim to support immunity, or L. acidophilus, which is found in miso and natural yogurt and is said to help digestion.
Bifidobacteria is associated with improved lactose digestion and can reduce symptoms of IBD. Lactose is the sugar found in milk products, and some of us have an intolerance that means our small intestine doesn’t make enough of a digestive enzyme called lactase, which helps break down lactose so our bodies can absorb it. Lactobacillus, meanwhile, is often used for culturing dairy products and benefits include improved digestion, the treatment of vaginal infections, lower cholesterol and the treatment of eczema in children.
“For most healthy people there is probably not much benefit to taking probiotic supplements every day because they only contain a relatively limited range of specific strains of bacteria which you may not be deficient in to begin with,” says Rice. “However, by eating a range of fermented foods every day you will improve the richness and diversity of your gut microbiome, which is likely to be more beneficial for our overall health.”
Amati agrees: “At Zoe, we recommend a whole food approach, and this is the case with probiotics, too. While there’s evidence that some probiotic supplements might have certain benefits – like Saccharomyces boulardii for diarrhoea – for sustained overall health, whole food and a healthy diet is the most important factor. And when you consume fermented plants like sauerkraut and kimchi, you get more strains plus the benefit of plant fibre and other healthy plant compounds.”
“Evidence suggests eating around three portions of fermented foods each day is beneficial,” observes Amati. However, even small changes can help. “Eating them regularly, even in smaller amounts, will still probably have a benefit. I love to eat natural yogurt with kefir, berries and almonds and add sauerkraut to my salads.”
Probiotic-rich fermented foods are becoming increasingly commonplace in supermarkets and include kefir, a fermented milk drink that you consume on its own. You can also buy thicker kefir, which has a similar consistency to yogurt and can be eaten the same way, either on its own or topped with berries and nuts.
Miso is made from soybeans, fermented rice and salt, and can be used in soups and sauces. Kimchi is fermented mixed vegetables, such as cabbage, cucumbers and leeks, in a mix of spices, while sauerkraut is fermented cabbage. Kombucha is fermented sweet tea, while some cheeses undergo fermentation and contain probiotics, such as Parmesan, certain cottage cheeses, and aged cheddar. Perhaps the best-known fermented food is sourdough bread. And apple cider vinegar, made famous by its celebrity fans like Victoria Beckham and Gwyneth Paltrow, who drink a shot of it in a glass of water each morning, is made by adding yeast to apple juice and allowing it to ferment.
“Apple cider vinegar contains a substance known as ‘the mother’, made up of proteins, enzymes and good bacteria that’s created during the fermentation process and it promotes a healthy microflora which supports gut health,” explains Gabriela Peacock, a celebrity nutritionist.
Lastly, don’t forget the basics when it comes to gut health. Government guidelines state we should eat 30g of fibre daily, which you can find in wholemeal or granary bread, plenty of colourful fruits and vegetables, and pulses such as beans and lentils.
Hamish began rearing quails for their eggs at age 11.