Despite a fondness for goose-liver pate, chocolate mousse and puffy pastries, the French have the lowest body weight per capita in the Western world. According to best-selling author and diet guru Michel Montignac, this proves that to eat well is to eat healthily. His latest book, "The Montignac Diet: Eat for Pleasure--Stay Slim Forever," will be released in 12 countries in February. Montignac spoke by phone from his country home near Geneva with NEWSWEEK's Eric Pape. Excerpts:

PAPE: What's your dieting philosophy?

MONTIGNAC: Weight gain comes from an excessive secretion of insulin. Understanding this means breaking with old ideas. Focusing on calories is a waste of time, as countless studies show. Since 1960, the number of calories consumed has fallen 25 to 35 percent and yet obesity rates have increased. A new study on France shows that between 1995 and 2003, the French consumed 6 percent fewer calories, but obesity increased 31 percent.

Why isn't exercise the answer?

People have tripled or quadrupled their sports activities since 1960. And in physical professions--plumbers, laborers and others--people are fattest, and the people who work in offices tend to be thinnest. The difference between them is how they eat. In the United States, the fatter you are, the poorer you tend to be. People don't get fat because they eat too much but because they eat badly. The best way to get thin isn't to eat less or to work out more, it is to eat better. If you choose food as I recommend, you can eat normally, be sated and lose weight. People always ask what quantities they should eat. I tell them that the quantity doesn't matter.

Why is French food healthy?

We use three times less sugar, less milk, more vegetables. Our fats are better--fewer trans-fatty acids. We eat fewer refined cereals in the morning and fewer sandwiches. And in France, 70 percent of the population makes lunch at home, which means less premade refined foods.

Are there problematic French foods?

There are too many fried potatoes. When I was young, people ate them maybe once per month, because cutting and frying potatoes required a lot of work. Mostly, we ate potatoes in soup. But fried, they are catastrophic. And the bread is too white in France. It is a cultural problem.

Does following your diet mean having to cook?

Anyone can make their own vinaigrette, their own omelet. Recipe books look complicated, but I make meals in 10 or 15 minutes, with fresh vegetables. It takes 30 seconds to make vinaigrette. I make a mayonnaise without a mixer in a few minutes.

Why doesn't rice make Asians fat?

It is an enigma. They rarely have diabetes or obesity. A study by Jenny Brown-Miller, an Australian professor, showed me that rice can be fine, as long as it is eaten with vegetables.

What other culinary ideas interest you?

I hold out a lot of hope for genetically modified foods. I am not afraid of a potato with the sugar level of a lentil. We have to be nuanced and we can't refuse science systematically, as some French people do. Perhaps companies like Monsanto and the Americans are moving too fast in commercializing it, but we don't need to return to the past. If we can use [special] bread with beneficial metabolic qualities to create a Pizza Montignac that is healthy, I am in favor of it.