A Gastroenterologist's Guide to Probiotics

Matthew a. Ciorba, MD


Clin Gastroenterol Hepatol. 2012;10(9):960-968. 

In This Article

Probiotic Concepts for Practice

What Makes a Probiotic a Probiotic?

Definitions of the terms probiotic, prebiotic, and synbiotic are provided in Table 1. This review focuses on probiotics, though some probiotics have been tested as part of a synbiotic product. Lactobacillus and Bifidobacterium species are the most commonly used probiotics. However, 1 of the first probiotics, which is still in use, is the nonpathogenic Escherichia coli Nissle 1917 (ECN). Most probiotics were initially cultured from humans and resemble known commensal gut bacteria. However, the commensal population they resemble typically represents only a fraction of the total luminal bacteria. Saccharomyces boulardii is a probiotic yeast strain with the potential advantage of having resistance to most antibiotics.

According to current definitions, probiotics should survive both gastric acid and bile to reach the small intestine and colon where they exert their effects. Clinical and basic investigations on probiotics have used a multitude of probiotic species, both as single strains and multispecies products. Many of these probiotics are available in a lyophilized (freeze-dried) pill form, though some are available in yogurt or as packets (sachets) which can be mixed into noncarbonated drinks. Whether synergism or antagonism exists between probiotic species when offered together has not been examined in clinical studies, though both scenarios are theoretically possible. Though not exhaustive, Table 2 lists several of the more commonly available probiotic preparations which have shown benefit in human trials. Probiotics are considered dietary supplements; thus, they are not covered by medical insurance and their production is not regulated by the Food and Drug Administration. As such, product quality, purity, and viability have been reported to be variable.[12] However, several clinically tested probiotic products with quality-controlled production are now marketed by reputable companies.

Does Any Yogurt Work Just like a Probiotic?

Lactic acid–producing bacteria have been used for centuries in food fermentation. Many yogurts contain live-active lactobacillus cultures and are considered functional food products; however, most are not considered probiotics per se. This term is reserved for products with an adequate number of microorganisms at time of consumption specifically shown to confer health benefits in controlled human trials. Yogurts fortified with an adequate number of viable bacteria shown to exert benefit in controlled trials are classified as probiotics. Given this information, and the knowledge that probiotic benefits appear species-specific, expected clinical end points may not be achieved by generically recommending yogurt to patients in whom a purported probiotic benefit is desired. It should be noted, however, that yogurt consumption has other benefits including improved lactose tolerance and the provision of protein, vitamin D, and calcium.

How Long Does One Have to Take a Probiotic?

As viable microorganisms, probiotics can survive in the human gut and impact microbes which colonize the gut. Probiotics are often detectable in the stool by culture or gene-based assays during periods of consumption. However, many probiotic strains do not colonize the gut and are no longer recoverable in stool 1 to 4 weeks after stopping consumption.[13] For example, McNulty and colleagues recently evaluated a fermented milk product with probiotic strains matching the commercially available Activia (Dannon, White Plains, New York). The investigators showed that the probiotic product did not change the gut's overall bacterial composition, but instead altered gene expression patterns relevant to carbohydrate metabolism in the host's resident gut microbes.[14] These changes in the human fecal "metatranscriptome" were transient, confined only to the time of the probiotic consumption. Thus, if sustained benefit from a probiotic is desired, continued consumption is likely required.

Where Can Probiotics Fit into a Therapeutic Algorithm?

Data for probiotic use in several GI disorders are reviewed in the following section. For AAD and viral gastroenteritis, supporting data are strong and probiotics are among the only treatment modalities available. However, the duration of symptoms in these conditions is typically short regardless of probiotic use. In ulcerative colitis (UC), pouchitis, and irritable bowel syndrome (IBS), adequate data exist for clinicians to consider recommending a therapeutic trial of specific probiotic strains or preparations in selected patients. In these conditions probiotics are usually administered as adjunctive therapy, rather than primary or first-line therapy. The decision to recommend probiotic therapy ultimately depends on the clinical scenario, patient interest, and clinician preference. In hepatic encephalopathy, Crohn's disease (CD), and Clostridium difficile–associated diarrhea (CDAD), conventional medical therapies remain the gold standard. Practice relevant probiotic concepts are summarized in Table 3.