quality-of-life indicators). Even within the gut, a wide range of end points have been tested. These include acute diarrhea, antibiotic-associated diarrhea, travelers’ diarrhea, C. difficile infection, lactose digestion, irritable bowel syndrome (IBS) symptoms, colic, inflammatory bowel conditions, and gut pain sensation.
In Sanders’s opinion, the field is embracing evidence-based approaches to conclusions on the health effects of probiotics, as demonstrated by the many systematic reviews and meta-analyses that have been published. As of November 2011 (the time of this IOM workshop), Sanders had identified 66 such reviews in the scientific literature. The end points cover a very broad range of body sites and conditions, including NEC; infant growth; persistent diarrhea; radiation-induced diarrhea; antibiotic-associated diarrhea; travelers’ diarrhea; H. pylori; Crohn’s disease, ulcerative colitis, and pouchitis; IBS; digestive symptoms; allergy; critical care or hospital infections; bacterial vaginosis; acute respiratory tract infections; and safety. Sanders noted that most of these end points are drug (i.e., can cure, treat, mitigate, or prevent disease) and not food end points. A common misperception is that a probiotic dose needs to be at least 109 in order to be effective, Sanders noted, but there is no single best minimum dose. Rather, whatever dose was used in the human study that showed a significant positive effect should be the minimum dose for that probiotic (Savino et al., 2007; Whorwell et al., 2006).
Significance of Strain Specificity
For the past 20 years, researchers have been emphasizing the importance of strain specificity. Plentiful evidence from animal models shows this to be the case, according to Sanders. The effectiveness of one strain of a species does not necessarily mean that other strains are equally effective. In a comparison of five different commercial probiotic preparations, Canani et al. (2007) observed variable effects on the duration of diarrhea in children, with only two of the commercial preparations demonstrating effectiveness (see Table 5-2). Sanders suggested that part of the reason that commercial products labeled as probiotic do not necessarily have similar effects could be that variable combinations of strains are used.
The challenge of strain specificity raises the question, Are there shared effects among phylogenetically related strains? For example, almost all studies on the two yogurt-containing probiotics Streptococcus thermophilus and Lactobacillus bulgaricus have demonstrated reduced lactose maldigestion in people who are lactose-intolerant. Regardless of strain, all yogurts containing at least 108 live starter S. thermophilus and L. bulgaricus per gram can bear the claim that the product will improve lactose digestion in individuals with lactose maldigestion (EFSA, 2010). Sanders asked, Could