The summer before starting Grade 9, Varsha Jayasankar of St. Catharines, Ont., was visiting family in southern India. She found herself eating a lot of mango ginger—a plant closely related to turmeric. “My grandpa was cutting it up and putting it in everything,” says Jayasankar, 17. “I said, ‘Why?’ He said, ‘To be healthy,’ ” referring to a long-held belief that the plant offers powerful antimicrobial benefits. Jayasankar set out to investigate: “I said, ‘I’ll prove you wrong.’ ”