Since most yogurt products contain active cultures anyway, is it really worth paying a premium for extra probiotic strains?
Probiotics are live bacteria and yeasts that are beneficial to health when eaten in adequate amounts.  They are usually eaten in yogurts or taken as food supplements, and are often described as “good” or “friendly” bacteria.
It is important for your large intestine to maintain a healthy count of these “good” 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 evidence seen so far is for the use of probiotics in the prevention of antibiotic-associated diarrhoea (ADD). A review of paediatric studies found that giving high doses of Lactobacillus rhamnosus and Saccharomyces boulardii when taking antibiotics can help prevent children getting ADD.  Without probiotics, the antibiotics tend to wipe out the protective gut bacteria, which results in diarrhoea.
In addition to this, when probiotics are given with antibiotics they reduce the risk of developing a Clostridium difficile (CD) infection by 64%.  CD are potentially dangerous bacteria that can multiply and cause a life-threatening infection if the balance of gut bacteria is disturbed by antibiotics. It is thought that probiotics directly kill or inhibit the growth of harmful bacteria in the gut.
Moreover, there is some evidence that probiotics can shorten a period of persistent diarrhoea by a day.  The strain Lactobacillus rhamnosus GG appears to help children with gastroenteritis caused by a rotavirus, and may also help people with traveller’s diarrhoea.
There is also some evidence, albeit weaker, to suggest that probiotics may help lactose intolerance and irritable bowel syndrome (IBS). Probiotics may also help protect premature babies from developing a dangerous gut disease.
The bacterial strain commonly used in yogurt, Lactobacillus acidophilus, can produce lactase enzymes. These enzymes are needed to break down the sugar lactose which is found in milk and dairy products. Therefore, people with lactose intolerance and children suffering from intestinal infection can usually tolerate yogurt with an active culture.
Probiotics may help reduce abdominal bloating and flatulence as well as provide general relief in some people with IBS. This is supported by a review of studies, but neither the extent of benefit nor the most effective species and strains are yet known. 
Some babies born prematurely are at risk of a serious condition called necrotising enterocolitis (NEC) – this is when tissues in the baby’s gut become inflamed and start to die. There’s some evidence that probiotics can reduce the likelihood of premature babies contracting NEC. .
Until 2010, the probiotic food industry claimed that their yogurts “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 or number of infections. 
There is no reason why healthy people should need to “rebalance their gut bacteria”, as some marketing material may claim.
There’s also no evidence to support claims that probiotics can help prevent and treat eczema in children. A review of twelve trials found that probiotics do not reduce eczema symptoms such as itching, nor do they change the overall severity of a person’s eczema. 
There have been suggestions that probiotics can help in the treatment of bacterial vaginosis or thrush, a condition is which the balance of bacteria inside the vagina becomes disrupted causing an unusual vaginal discharge. However, there’s currently no evidence that eating yogurt or inserting it into the vagina will treat thrush or relieve its symptoms.
Some studies have shown that by regulating intestinal transit time, probiotics may improve constipation among the elderly. In particular, B. lactis DN-173 010, L. casei Shirota, and E. coli Nissle 1917 have shown to increase defecation frequency and improve stool consistency. However, a review of studies in adults and children published in 2010 concluded that their effectiveness for constipation hasn’t been demonstrated. 
It is worth pointing out that different bacterial strains are effective for different health functions. Don’t assume that a yogurt containing active live culture will necessarily offer all of the above health benefits.
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” yogurts and supplements sold in shops, which may not live up to the advertised claims.
In general, probiotics are regulated as foods, and don’t undergo the rigorous testing and approval process that medicines do. This means we don’t know whether a probiotic yogurt, supplement or tablet contains exactly what is stated on the label and whether the amount of “good” bacteria in it is enough to have a beneficial effect.
However, what we can say is that probiotics appear to be safe. So if you wish to try them at least they shouldn’t cause any unpleasant side effects!
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