There is a growing body of knowledge that simplified diets (high fat, high sugar, low fiber) negatively affect aspects of gut barrier function including increased susceptibility to transient and persistent colonization of extra-intestinal pathogenic bacteria, changes to gut barrier morphology, innate and acquired immunity and pro-inflammatory state of the gut. The book discusses natural products such as polyphenols, anthocyanins, flavonols, proanthocyanidins, and hydrolyzable tannins as a whole food approach or as supplements to simplified diets, and the role they play in modulating these aspects of gut barrier function.