For a bacterium to be called ‘probiotic’ it must be alive and deliver benefit to the host species, this is a definition set down by the World Health Organisation (WHO). Any bacteria which do not deliver benefit are not probiotic, similarly it is wrong to refer to freeze-dried, deactived bacteria as probiotic. They only become probiotic if they return to life and begin to divide and confer benefit.
An alternative question to the one in the title would be to ask ‘which strains of probiotic bacteria confer most benefit to the host?’
This is the holy grail of probiotic research and the subject of many a study, to date there is no single answer. One reason for this is that a healthy human gut contains more than 350 different types of bacteria, some of which are essential to health, and so could be considered probiotic and others which simply use the gut as their home without any particular interaction with the host; us. These bacteria are not evenly distributed, different types or strains as they should be called are adapted to live in different parts of our digestive tract.
Humans are essentially a long tube with a mouth at one end and a bottom at the other. The digestive tract connects the two and if it was removed and uncoiled would be about eight metres long. Not only is it long, but thanks to the various folds and creases on its inner surface if it was flattened out it would have the surface area of a tennis court.
The characteristics of this tube vary along its length. Starting at the mouth, a tube called the oesophagus leads to the stomach. The stomach is an acidic environment where there are also various enzymes present depending on whether food is present or not. The pH of a human stomach contents can be as low as 1 due to the hydrochloric acid present, this is the same acid as is used in car batteries! After the stomach, there is about six metres of coiled small intestine. Bile acids from the liver are released into the small intestine and among other things this increases the pH inside the tube making the environment less acidic. In the jejunum, the middle part of the small intestine, the acidity is about the same as orange juice at pH 4 to 5.
The small intestine eventually opens up into the caecum which is the first part of the colon. The colon is a larger diameter tube, around 1.5 metres long which serves to absorb water from the contents of the tube and firm this up ready for evacuation through the rectum and anus. The pH within the colon is fairly neutral at around 7, and most of the nutrients within the food passing through the digestive tract have already been absorbed into the body.
Different bacteria inhabit the entire length of the digestive tract. In the oesophagus Steptococcus can be found, the highly acidic stomach might be expected to be devoid of life, but in fact Gram-positive bacteria as well as Proteobacteria, Bacteroidetes, Actinobacteria and Fusobacteria can all live here. The more hospitable small intestine is home to Enterococci and Lactobacilli, four strains of which are contained in Symprove. Finally the colon supports the greatest range of bacteria with representatives of more than 300 species present including Enterococci and Lactobacilli.
Trying to sift through all the different species of bacteria in different locations within the GI tract and work out what does what is a task beyond even modern research techniques. The complex interactions between species complicates things further. What we do know has been learnt through trial and error and by administration of different probiotics and close monitoring of the results.
Two things are clear though, for a probiotic to work it needs to reach the lower parts of the digestive tract, after the stomach, and it needs to be alive and able to rapidly divide and establish a population in the small and/or large intestine. Symprove contains four strains of live Lactobacillus and Enterococcus probiotic bacteria. These are able to survive the hostile environment of the stomach to reach and then populate the small and large intestine.
No other probiotic can claim to do this because no other probiotic contains four strains of live, activated bacteria. So when you drink Symprove you are giving probiotics the best possible chance of working for you.