In this interview, Sally Norton, author of “Toxic Superfoods: How Oxalate Overload Is Making You Sick — and How to Get Better,” reviews how and why even foods we’ve been told are healthy can wreak havoc on your health. As the title of the book implies, the main culprit in question is oxalate or oxalic acid, found in many plants, beans, grains, seeds and nuts, fruits, berries and herbs.