The question of what role intestinal bacteria play in human health has grown in popularity recently, because of the rise in “gut-healthy” consumer products and increased research into the ways the gut affects various systems in the body. This term has raised questions about the role that probiotics and prebiotics play in shaping the health of that gut health and how fermented foods-a centuries-old staple now heavily marketed to consumers—might also affect the composition of the microbiota. Various studies on probiotics, fermented foods, and gut health are examined to determine the extent to which the gut really plays a major in human health and whether products marketed for gut health actually alter its makeup. In general, evidence about such products is inconsistent, and conclusions are varied. Many studies show links between the profile of the intestinal microbiota and digestion, disease states, and even mental health. Probiotics, in general, have been determined to positively boost the levels of Lactobacilli, Bifidobacteria, and Streptococci in the gut, which may increase the positive effects of the microbiome. However, other fermented foods such as kombucha, kimchi, and tofu, which are often marketed as containing probiotics, require more human subject studies to draw concrete conclusions about these supposed benefits.