The first 1,000 days are a critical period for maternal, fetal, infant, and toddler nutrition. A good microbiome allows for a healthy immune system. Renowned professor of pediatric gastroenterology and nutrition, and endowed chair in pediatric research, Fayez K. Ghishan, MD, discusses the important role gastrointestinal microbiota plays in the development of immune function. The properties of probiotics are strain-dependent and are not all formulated the same. Dr. Ghishan discusses the mechanisms and other factors that influence probiotics’ clinical benefit to gut health and the immune system of newborns. He explains the unique properties of the probiotic strain Lacticaseibacillus rhamnosus GG and its impact on tolerance to cow’s milk protein. Dr. Ghishan also reviews the most recent and pertinent studies of LGG®, while discussing the role of LGG® in the future of allergy management.