The probiotic LGG works by making resident gut bacteria produce anti-inflammatory products. How do probiotics work? Do they do anything or am I flushing money down the toilet? Lactobacillus rhamnosus GG (LGG), one of the most common probiotics available, can improve a variety of digestive disorders [1, 2], psychiatric disorders [3], and atopic dermatitis [4] in infants and children. LGG does not “move in” and establish residence in the gut [5]. It simply passes through. Findings from this study by Eloe-Fadrosh et al. suggests that probiotic bacteria may not need to take up residence in the human gut to be helpful, but that these effects are variable among individuals. Claire Fraser’s research group at the University of Maryland, Institute for Genome Sciences and colleagues at the Massachusetts General Hospital for Children examined samples from an open label study (people knew they were taking a probiotic) to assess safety of the probiotic LGG [6] in healthy, elderly patients. Fecal samples of 12 healthy adults (7 females and 5 males) ages 65 to 80 were collected prior-to, during, and one month after taking the LGG probiotic twice daily. The number of different types of bacteria and genetic activity of the microbiome was compared within and