After examining how people buy food in an aisle-by-aisle guide called What to Eat , Marion Nestle picked up a can of pet food to see how its ingredient label compared with the ones on human chow. Nestle, a professor of nutrition, food studies and public health at New York University, found the pet-food ingredient label incomprehensible. This led to her latest book, Feed Your Pet Right: The Authoritative Guide to Feeding Your Dog and Cat (Free Press, 2010), written with Malden C. Nesheim, professor emeritus of nutritional sciences at Cornell University. Nestle spoke with TIME about navigating the maze of pet-food products in what has become an $18 billion industry in the U.S.

What most surprised you in writing this book?
We were surprised by the lack of research on important questions. We were very eager to compare the longevity of pets based on their diets, whether they were fed raw, vegetarian, premium or complete and balanced pet-food products. We were unable to find any research that compared pet foods in this way. It was very frustrating. Of course, pet-food companies don't conduct this type of research!