Over a lunch of goat cheese ravioli, mackerel tartare and halibut with heirloom tomatoes, Guiliano, author of French Women Don't Get Fat: The Secret of Eating for Pleasure, explained the seemingly impossible.

PW: What's one of the biggest differences between the way Americans and French people eat?

Mireille Guiliano: We eat a lot of fruits and vegetables, which Americans don't do. Even some young people in my office, they order pizza for lunch every day. That's not good. And isn't that boring after a while? They don't pay attention. It's a mindless action. The portions are very important, too. Scientifically, it has been proven that after three bites, your palate has been satisfied. It doesn't matter what you eat. So if you eat one boule of ice cream, that's all you need. You don't have to eat pint after pint after pint.

What about the other diets out there? Why is there always a "next big thing" when it comes to losing weight?

I don't know, but it's only getting worse, I think, these diets that don't work. People are unhappy when they are on diets, because it's don't do this, don't do that, do this, do that. Each of us is different. So we have to do the things that work for each of us. And then once you know it, it's really tricking your mind. It's like a game.

At the end of the day, it's your choice. We only have one body, and you have to show respect for it.

You advise readers not to "multitask" while they eat—no TV, newspaper, or eating at the wheel or on the subway.

That's why we sit down. Nobody among my friends in Paris would think about having a good bottle of wine and sitting and watching TV. With technology, there is so much isolation with people now, that there are very few places where you can connect. Food and eating is all about conviviality.

What do you say to people who say French women don't get fat because it's genetic?

It's not true. It's very simple: if you take in more than you burn out, you're going to gain weight, no matter what your metabolism is like.

What about French men? Do they get fat? And can men follow the same instructions as women?

Actually, the man who did the illustrations for my book, he read the book and then he called me three weeks later, and he said, "I have to tell you, this book changed my life." He is eating fresh food from the market, drinking more water... it works!

The recipes in your book more closely resemble the recipes found in classic French cookbooks than average diet books.

Oh, no, no! They are basically home cooking, they are from my aunts, my friends, in Paris and Provence.

Translation rights have been sold in Germany, England, Spain, Japan and elsewhere. Will you bring the book to France?

Yes, I think so. Things in France have changed. Now when you go to the supermarket in France, it's an hypermarche. For example, with packages of yogurt, they have copied American words. It's not as bad as here, but it's a big box, and it's loaded with sugar. The chicken, it's really bad. Obesity is rising there. I know what they should retitle my book, if it is published in France. It should be, it's hard to translate, but it would mean "These French Women Don't Get Fat." It's for the other ones who get fat.