The correct option is indeed statements 1 and 3. Probiotics are live microorganisms, including both bacteria and yeasts, that can confer health benefits, particularly in digestive health. They are commonly found in fermented foods, such as yogurt, and help in the breakdown of lactose, which is the sugar found in milk, thereby aiding digestion for individuals who may be lactose intolerant. In contrast, statement 2 is incorrect because many probiotic strains do naturally inhabit the human gut, contributing to a balanced microbiome. Understanding the role of probiotics thus highlights their importance in nutrition and gut health, which is relevant for UPSC preparation focused on health and wellness.