(FORTUNE Magazine) – Pork-barrel politics are nothing new to Marion Nestle. When she moved to Washington, D.C., in 1986 to help craft the first Surgeon General's Report on Nutrition and Health, she was told point-blank that the report could not recommend that Americans eat less meat, sugar, or--for that matter--any other food. In her book Food Politics: How the Food Industry Influences Nutrition and Health, which will be published in March by the University of California Press, Nestle, 65, details the power of the food lobby. FORTUNE caught up with her to talk about ketchup, the dark forces at work behind the food pyramid, and Monica Lewinsky.

Q: How much does Enron's access to high-ranking government officials remind you of the food industry?

A: Been there, done that. The food industry is no different. One of the most famous incidents was when the CEO of a sugar company called and interrupted a tryst between President Clinton and Monica Lewinsky. He called on a holiday and got put right through to the President.

Q: You claim that the U.S. produces 3,800 calories per day per person--twice what we need. Where's all that food going?

A: The data on activity show that people are as sedentary now as they were 15 years ago. But people are eating more, and so it's going to their waistlines.

Q: Can't individuals control what they eat?

A: One of the things that surprises me is how ubiquitous food marketing is and how little it is noticed. Larger portions are brilliant marketing. There's something about human psychology--if a lot of food is put in front of us, we eat it. People who believe our eating habits are a question of individual free will are much, much stronger than I am.

Q: What are some of the craziest food health claims that have been made?

A: Where did anybody get the idea that ketchup could cure cancer? They also tried to get ketchup declared a vegetable in the school lunch programs. Someday I'm going to write a political history of ketchup.

Q: What about the push for more calcium-fortified foods? Is there a lobbying group to thank for that?

A: There isn't a single food or nutrient that does not have its own lobbying group. These groups watch everything that the government does with intense scrutiny. Anything that indicates a government agency may say "eat less," they're right on top of it.

Q: Those are the industry's dirty words, right?

A: Eating less is what they're trying to avoid. But if you're worried about our population and obesity, that's the message that needs to be delivered.

Q: Does anyone use the food pyramid anymore?

A: It's hard to say. When you drop the pyramid, which has basically no advertising, marketing, or educational budget behind it, into $30 billion a year in marketing for products like potato chips, it's easy to say nutrition education doesn't work. Altoids has a $10-million-a-year advertising budget. That's five times what the National Cancer Institute and the Produce for Better Health Foundation spend to encourage consumers to eat five fruits and vegetables a day.

Q: We hear a group wants bottled water added to the pyramid when it is revamped in 2005. Anything wrong with that?

A: The exercise people want somebody climbing up the pyramid, and the alcohol people want a glass of wine in the pyramid. Water is fine, but it doesn't have to be from a bottle.

Q: So are you related to the Nestle food corporation?

A: [No.] The family legend is that there was a Nestle's milk poster on the wall at Ellis Island, and they thought it must be a good American name and they took it.