The most widely accepted definition for probiotics is the one proposed by the Food and Agriculture Organization/World Health Organization working group and recently reaffirmed by the International Scientific Association for Probiotics and Prebiotics: live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. The definition thus highlights three major points: the viability of the microbes, the dose, and the documented health benefit.
Digestive health should be defined through the absence of intestinal complaints. This is clearly not satisfying, but may work from a practical perspective. Most healthy consumers will be happy with their digestive health if they are not having any symptoms, that is, are not reminded of their intestines in the first place.
Therefore, digestive health therefore focuses on reducing risk for gastrointestinal disturbances and/or relieving such symptoms if and when they occur. This is discussed in the next section.
Although probiotics can be used as a drug, most probiotics are marketed as food ingredients or as dietary supplements. As such, probiotics are not expected to prevent disease, they may reduce the risk of disease. Probiotics do not treat or mitigate disease, they may relieve symptoms of disease. Therefore, most probiotics are not treated as drug, their main aim is to maintain health. Furthermore, traditional fermented foods as such yogurt, sauerkraut, and kimchi are not probiotics, unless they contain specific strains with documented health benefits such as certain probiotic yogurts.
Constipation, Slow Intestinal Transit
Constipation is one of the most common digestive disorders. Although benign, constipation has a substantial influence on general well-being and is considered as a risk for certain serious intestinal conditions such as diverticulitis. Constipation is defined as three or less spontaneous bowel movements per week. It is more common in females than in males and tends to increase with age.
A number of probiotics have been tested for their effect on slow intestinal transit; most of them are Bifidobacterium lactis strains, such as B. lactis DN-173010, B. lactis HN019, or the combination of Bifidobacterium longum BB536 and B. lactis 420. In general, the tested probiotics have been found to shorten colonic transit. Important here is that the probiotics do not shorten the transit time of subjects with “normal” initial transit times, that is, they do not cause diarrhea. Probiotics have also been shown to improve stool frequency and consistency. Although studies have used many different doses, meta-analyses have failed to observe a dose–response effect.
Antibiotic-associated diarrhea (AAD) has been reported to occur between 5% and 39% of patients on antibiotics. The most common pathogens causing AAD are assumed to be Clostridium difficile, Clostridium perfringens, and Staphylococcus aureus. However, these pathogens do not account for all AAD and thus many unknown causes remain; some of which may be nonmicrobiological and relate to physiological changes in the host (eg, changed bile acid resorption).
Community-acquired diarrhea can be caused by a multitude of pathogens, toxins, and other factors. Some of the best investigated community-acquired diarrhea targets for probiotics are rotavirus diarrhea and traveler’s diarrhea.
L. rhamnosus GG is an example of a probiotic that has been shown to reduce the risk for rotavirus diarrhea in children in a hospital setting (ie, a nosocomial infection) and has also been observed to aid in the treatment of rotavirus diarrhea. In community-acquired diarrhea, the etiology is often not determined, but also with these diarrheas, probiotics such as B. lactis HN019 or L. paracasei Lpc-37 have been observed to be successful in reducing risk, especially in young children.
Irritable Bowel Syndrome
Irritable bowel syndrome (IBS), not to be confused with inflammatory bowel disease (IBD), is not a disease but a syndrome. Probiotics appear to have potential in relieving specific symptoms of IBS, such as abdominal pain (eg, VSL#3 or Bacillus coagulans GBI-30, 6086), bloating (eg, L. acidophilus NCFM + B. lactis Bi-07 or B. bifidum MIMBb75), and flatulence (eg, S. boulardii). Overall improvement in IBS quality of life, however, appears to be challenging.
Necrotizing enterocolitis (NEC) is a very serious condition with a high mortality rate. The main risk group is very low birth weight infants (<1500 g). The intestinal microbiota of preterm infants has been reported to be less diverse than that of term infants and appears to be more commonly colonized by potential pathogenic species from genera such as Klebsiella, Enterobacter, and Clostridium.
Inflammatory Bowel Disease
IBD can be divided into three different conditions: ulcerative colitis, which is an inflammatory condition limited to the colon; Crohn’s disease (CD), which is an inflammation that can be anywhere in the intestinal tract; and pouchitis, which is an inflammation of an ileoanal pouch. The main probiotics studied are Escherichia coli Nissle 1917 and the probiotic combination VSL#3.
Helicobacter Pylori Eradication
Helicobacter pylori is a common inhabitant of the gastric mucosa and has been found to be associated with gastric ulcer and gastric cancers. However, H. pylori has a dual role: exposure to the organism has been found to correlate with reduced risk for atopic dermatitis in children and eradication of H. pylori has been suggested to correlate with an increased risk of obesity. While in vitro and animal studies have indicated antagonistic activities toward H. pylori by, in particular, Lactobacillus probiotics, this has not been replicated in humans. Probiotics can therefore not be considered as an alternative for standard therapy. Some strains such as Lactobacillus johnsonii La1 have been observed to reduce H. pylori numbers and activity, which may actually be preferable in light of the potential positive role the organism may play.