Over the course of her career, journalist Gina Kolata has made it her mission to challenge many of the basic assumptions about dieting, health and fitness in America. Dr. Oz talks to Gina, a New York Times science writer, about some of her groundbreaking books and surprising finds.

In Rethinking Thin, Gina takes a closer look at society's obsession with weight loss and explores some of the myths and realities about dieting. She says that while many Americans struggle with weight, they take unrealistic cues from the media exposure of certain celebrities about what an ideal figure should be.

For example, Gina says that actress Jennifer Aniston, who has a body mass index of 18.3, has been portrayed as having a perfect figure—yet Gina says Jennifer's "really, really, really skinny" physique is completely unattainable for most Americans. "Even if you're a normal weight and you can't achieve it, you say, 'I'm still fat, I don't look good,'" she says. "It's crazy."

Busting commonly held beliefs about fitness and exercise is the topic of Gina's book, Ultimate Fitness. Gina says that while she is an avid runner and enjoys working out, she was surprised by some of her findings, including the discovery that vigorous exercise—such as jogging—may not provide a greater health benefit than if you simply walked briskly on most days. "You get almost all the benefit from doing moderate exercise, and as you add more intense exercise, you get diminishing returns," she says.