The scientists discovered that the probiotics successfully colonized the GI tracts of some people, called the "persisters," while the gut microbiomes of "resisters" expelled them. Moreover, the persister and resister patterns would determine whether probiotics, in a given person, would impact their indigenous microbiome and human gene expression. The researchers could predict whether a person would be a persister or resister just by examining their baseline microbiome and gut gene expression profile.
The best case for probiotic therapy has been in the treatment of diarrhea. Controlled trials have shown that Lactobacillus GG can shorten the course of infectious diarrhea in infants and children (but not adults). Although studies are limited and data are inconsistent, two large reviews, taken together, suggest that probiotics reduce antibiotic-associated diarrhea by 60%, when compared with a placebo.
Two dangerous diseases in newborns, necrotizing enterocolitis (NEC) and neonatal sepsis, may meet their match with well-designed probiotic supplements. Both of these conditions are common in premature babies and are most dangerous in low birth weight and very low birth weight infants. Research has confirmed that when a pregnant mother takes high-quality probiotics during pregnancy, her baby is significantly less likely to develop either NEC or sepsis, particularly when the baby is breastfed after birth (and mom is still taking the supplements) and/or when probiotics are added to formula. A probiotic supplement with multiple strains seems to be the most effective in these cases.
As with other types of supplements, scientists are still discovering the full potential of probiotics. However, when taken regularly, it is believed that they help support digestive health by helping maintain the balance of beneficial and non-beneficial bacteria in your digestive tract. Having a natural balance of good bacteria in the digestive tract can help defend against occasional digestive issues. In addition, probiotics play an important role in supporting immune health, since 70% of the body's immune system is found in the digestive tract.∗