What are prebiotics?
Prebiotics are carbohydrates that "friendly" gut bacteria feed on. They're found in tomatoes, asparagus, onions, garlic, artichoke, chicory and bananas, and reach the gut relatively unchanged as the body cannot digest them.
It's believed that eating prebiotics causes more protective bacteria to grow in the gut.
Probiotics are live bacteria and yeasts promoted as having various health benefits, including preventing and treating a range of conditions. They are usually eaten in yoghurts or taken as food supplements, and are often described as "good" or "friendly" bacteria.
Probiotics are thought to help restore the natural balance of your gut bacteria when it has been disrupted. However, there is little evidence to support most health claims made for them.
The strongest of this evidence surrounds the use of probiotics in the prevention of antibiotic-associated diarrhoea (AAD).
There's also evidence, albeit weaker, to suggest they may help in treating irritable bowel syndrome (IBS), lactose intolerance and a complication of ulcerative colitis treatment. It is also thought that probiotics may help protect some premature babies from developing a dangerous gut disease.
However, until more research is carried out, it's uncertain whether the benefits stretch any further than that. Generally, it's hard to see how swallowable bacteria could have an effect on conditions outside of the digestive tract.
It should also be noted that there's likely to be a huge difference between the pharmaceutical-grade probiotics that show promise in clinical trials and the "probiotic" yoghurts and supplements sold in shops, which may not live up to the advertised claims.
The problems with "probiotic" yoghurts and food supplements
Until 2010, the probiotic food industry claimed in adverts that their yoghurts "boost your immune system". However, these claims were ruled unproven by The European Food Safety Authority and are no longer allowed to be made.
Not only is there a lack of evidence for the supposed immune system benefits of probiotics, but research found that in healthy children, probiotic supplements had no effect on antibody levels, days of fever and number of infections.
More research is needed before we can draw any conclusions, and the vague term "boosting immunity" needs clearly defining so we can understand exactly what beneficial effect, if any, probiotic foods and food supplements have on the immune system.
There's also no reason why healthy people should need to "rebalance their gut bacteria", as some marketing material may claim.
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