Rarely a month passes without a new piece of research extolling the possible virtues of probiotics.
The latest? Consuming probiotic supplements daily for just three weeks can encourage weight loss, according to a new study review from the Vestfold Hospital Trust in Norway. Beyond the impressive-sounding headline, however, it's worth noting that the effects were relatively small, and the scientists say more research is needed to confirm the initial findings.
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So what exactly are probiotics?
Probiotics are live bacteria and yeasts – otherwise known as 'good' or 'friendly' bacteria. They're commonly added to yoghurts or taken as food supplements. Their primary purpose is to restore and maintain the natural balance of gut bacteria in the stomach and intestines, particularly if it's been disrupted by illness or treatment.
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What are the proven benefits of probiotics?
There's sound evidence that probiotics can prevent or treat diarrhoea. In particular, they can reduce the risk of developing a C.difficile infection – a potentially serious bowel condition that sometimes affects people who have been treated with broad-spectrum antibiotics. C.difficile risk is much higher among the over-65s. So if you've been prescribed antibiotics, do ask your doctor whether you should take probiotic supplements, too.
Taking probiotics can also help reduce IBS symptoms, such as bloating and flatulence, according to a 2010 study review. The problem? They don't necessarily work for everyone with IBS. So the National Institute for Health and Care Excellence (NICE) advises taking them for at least four weeks to see if they may be beneficial for you.
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Finally, certain probiotics – such as Lactobacillus acidophilus – appear to ease symptoms of lactose intolerance. This is a relatively common digestive problem in which the body can't digest lactose, a type of sugar found in milk and dairy products. Symptoms include diarrhoea, stomach cramps and flatulence. So if you're lactose intolerant, you could try a probiotic preparation of Lactobacillus acidophilus.
Do probiotics benefit healthy people?
If you're perfectly healthy, there's so far little convincing evidence to suggest you'd benefit greatly from taking probiotics – simply because your gut bacteria doesn't need rebalancing. This was the conclusion of a 2016 study review from the University of Copenhagen.
Bear in mind, though, that the researchers only looked at seven previous studies – each of which used different probiotics containing different friendly bacteria in various forms. So we're back to the same old caveat: more research is needed before we know for sure whether the health claims made for each specific probiotic are definitely correct.
It's worth noting, for example, that widely made claims about the immunity-boosting benefits of probiotic yoghurts were ruled unproven by the European Food Safety Authority in 2010. These claims can no longer be made on the packaging unless more robust research proves them to be true.
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What other health claims are made for probiotics?
There's a possible link between probiotics and sleep, for instance: various studies have suggested that multi-strain probiotics may boost the production of hormones needed to encourage restful slumber.
Researchers found that people who ate more fermented foods had fewer symptoms of social anxiety.
A 2015 US study identified a potential connection between fermented foods, which contain probiotics, and social anxiety. Researchers found that people who ate more fermented foods had fewer symptoms of social anxiety – leading them to suggest that microorganisms in the gut can somehow influence the mind.
Similarly, a University of Missouri study found a link between probiotics and reduced stress levels. Before you get too excited, we should point out that the study was carried out on fish, not people, although the researchers hope the results could be replicated on humans in future. So watch this space!
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Anything else I should know about probiotics?
Remember, probiotics are usually classed as foods, which means they don't undergo the same rigorous testing as medicines. So, warns the NHS, we can't always be sure the product contains the bacteria stated on the label and enough bacteria to have an effect, or that the bacteria will survive long enough to reach the gut. And there are lots of different types of probiotics so effects and benefits will differ from one product to another.