The human digestive tract is full of bacteria that help it work properly. The vast majority of those bacteria are helpful, but there also some that can cause problems. The key is to keep them in balance. Often in gastrointestinal illnesses, amongst many other problems, this fine balance can be disturbed. In some illnesses a disturbed balance of bacteria is the primary cause (for example food poisoning). In other illnesses however the change in bacteria is due to the illness rather than the cause of the illness. This is an important difference.
Probiotics are live bacteria that aim to have a positive effect on human health. There are many products with probiotics available. But they are all very different in ingredients and concentrations. Many are very weak or contain bacteria, which have not been shown to help. Often the producers make health claims with little evidence to back them up.
In some conditions probiotics can be really helpful and even more powerful than antibiotics, while in other conditions they may even be harmful. Often there is little guidance available to the consumer. Dr Selinger has conducted research into probiotics himself and understands the complicated evidence situation. He can advise you whether probiotics are helpful for your condition and which product has evidence for its effectiveness.
As a strong believer in evidence based medicine Dr Selinger believes that probiotics should be scrutinised in the same manner that drugs are.