The role of bacteria within the GI tract has fascinated the public for years. Enteric infections such as Shigella, Salmonella and Campylobacter which cause intense diarrhea, bleeding and fever have been described over the past 75 years. More recent additions include E. coli O157 and Clostridia difficile. In 1983 Helicobacter pylori was described as an infection in the stomach which causes duodenal ulcers.
In this past decade the beneficial role of bacteria within the colon or large intestine has been clarified. Microbiome is the accepted term for the normal population of bacteria within the small and large intestine. In the stomach there are few, if any, bacteria due to the very low pH. With progression through the small intestine there are low numbers of bacteria (about 100 per milliliter) with increasing concentration to 1000-100,000 bacteria per milliliter in the distal small bowel. In the colon the concentration of bacteria increases astronomically to 10-10 trillion bacteria per milliliter. There are more than 1000 species of bacteria reported within the colon and more to be identified. These bacteria take advantage of different ecologic niches within the colon. Interestingly, the population of bacteria within the colon is established very shortly after birth and is very similar to the bacteria that your mother maintains within her colon.
The microbiome remains stable throughout your lifetime except for major events related to use of antibiotics or pathologic infections such as Salmonella. In these circumstances there is a major disruption which is usually temporary. Typically the normal population of bacteria reestablishes itself within a short time. There is accumulating research that changes in the microbiome can lead to alterations in GI tract function and can be manifest by GI symptoms such as flatulence, abdominal bloating, constipation or diarrhea.
Bacteria that are ingested that favorably influence the microbiome are called probiotics. Probiotics have played a role in human nutrition for millennia. Yeasts have been used in the production of bread for more than 5,000 years allowing bread to leaven, to make it rise. These same extracts of yeast have been used to ferment various substances into alcohol beverages – ale, beer, wine. (As an interesting side note in all archaeological studies to date wherever a bakery was identified a brewery was always located nearby.) Other examples of probiotics include bacteria used in various yogurts – fermented milk products of cows, goats and horses. Aside from the nutritional benefits of these products it has been observed that these products can have a beneficial effect on the GI tract specifically relieving bloating, altered bowel habits (diarrhea and/or constipation). It was in 1900 that Elie Metchnikov, a Nobel laureate, proposed the term probiotic to describe a bacteria which is not a usual resident of the colon that can be administered orally, establish a presence within the colon and have a favorable influence on overall health.
Prebiotics are foods that influence the bacteria within the colon in a favorable fashion. Typically these foods include fiber of various sorts such the soluble and insoluble fibers that are present in fruits and vegetables. Alternatively manufactured fibers such as Citrucel, Metamucil or Benefiber would qualify as well. A recent trend has been the production of short chains of sugar molecules which are not naturally occurring called oligosaccharides some of which have been patented. The beneficial effect that is desired may relate to regularity, reduction of bloating. Unfortunately the actual effects of prebiotics on specific bacterial flora within the colon is not well studied so it is difficult to determine if any benefits are related to changes in the bacterial flora.
A frequent question posed is should I take probiotics and/or prebiotics on a routine basis to enhance my health? Currently there are no well done medical studies that would justify this intervention. There are very specific medical conditions such as colitis that may benefit from the use of probiotics but this is an issue that should be discussed with your physician. Accumulating information indicates that certain probiotics may well improve abdominal symptoms such as bloating. Unfortunately the studies that have been reported to date have not been high quality often being very short term in duration with small numbers of subjects thereby limiting the value of these studies and their applicability to the general population. At this point no recommendations can be made for the routine use of probiotics or prebiotics except to follow your mother’s advice: Eat your fruit and vegetables!