Sept. 27, 2007  -- In a world of fad diets and ever-changing ideas on how to get thin, Gary Taubes is not just another diet guru but a journalist who has covered science for the past 30 years.

It was Taubes who wrote the eye-opening -- and controversial -- New York Times magazine cover story five years ago that asked the near-blasphemous question: "What If Fat Doesn't Make You Fat?"

Now he's at it again. He's expanded that article into a new book, "Good Calories/Bad Calories: Challenging the Conventional Wisdom on Diet, Weight Control, and Disease." In the book, Taubes looks back at some 50 years of scientific research on why we get fat. He blames the bread.

"My wife likes to refer to me as the Grinch who's trying to steal Christmas," Taubes said.

And not just the bread, but the whole family of complex carbohydrates. So "Nightline" took Taubes to lunch, and what better place to discuss the dangers of carbohydrates than Raffaele's, an Italian restaurant on Manhattan's East Side, where we could talk -- over bread and pasta -- about carbs and fat, good science versus bad.

Carbohydrate Chemistry

Taubes said that after rereading years of scientific research, he has found proof that for the last half century, science has just gotten it wrong: It's not fat that is making Americans fat, he said, it is the base of the food pyramid, the complex carbohydrates, foods such as bread, pasta, potatoes. It's the starches we were told we needed that make us pudgy.

It's simple chemistry, said Taubes. Carbs spike insulin. Insulin creates sugar. And sugar packs on the pounds.

"The grains are carbohydrates," Taubes said. "They're refined carbohydrates. You take off the shell and all the protein and the vitamins, and you refine it down, and you end up with something that its primary effect on the body, immediate effect, is to raise insulin levels. And if you raise insulin levels, what that does is drive calories into your fat tissue. Raising insulin literally works to make you accumulate fat. This is one of these phenomena that for some reason the medical research establishment has chosen to consider irrelevant to why we get obese."

It's a theory that Taubes claims is simple -- and anthropological. It evolved from our days as hunter-gatherers, before we ate refined carbohydrates and sugars.

"And all we're saying [in the book] to do is, 'Don't eat these foods we didn't evolve to eat.' It's conceivable that switching to a diet absent these foods, making the transition has side effects that we have to deal with, that doctors have to deal with," he said. Click here to read an excerpt of Taubes' book.

Carb-Eating Cavemen

"Carbs are not killers," said New York nutritionist Carol Forman Helerstein. "Mother Nature would not have put carbs on the face of the earth if they were killers. If you go back to our ancestry and you look at the caveman, what did he eat? He ate carbs."

He ate carbs in the form of fruits and vegetables, said Helerstein, and not all carbs are created equal. "[T]he difference is that today the carbohydrates, because they're processed by the food manufacturers, are very high in sugar. And the scientists have a name for that: high gylcemic index -- it just means that it has a lot of sugar in it. So there's a difference between a Milky Way bar and a lettuce leaf, but they are both carbohydrates. So if you are eating the right carbohydrates, the ones that come from the natural sources, the fruits and the vegetables, then you will have a healthy diet."

Helerstein is the chief nutritionist for Diet Chefs, a multimillion dollar company that delivers prepared meals to customers' homes, meals based on the company's 40-30-30 formula: 40 percent low-glycemic "good" carbohydrates, 30 percent lean protein and 30 percent "good" fat. Standing at a table filled with Diet Chefs meals, Helerstein points to a typical Diet Chefs dinner.

"This would be a typical, wonderful meal that any scientist would be happy to eat," Helerstein said. "You have got your basic protein in your chicken. Now that's a lean protein chicken. Your carbohydrates are coming to you from the natural carbohydrates, which in this particular case is salad and vegetables, and then in your dressing here there's a little bit of olive oil and some flavoring that you're able to pour over your salad and you have each of the protein, the carbohydrate and the fat. That keeps your insulin levels stable and that's what health is all about."

Controversial Theories

Helerstein and Taubes agree that the low-fat proponents got it wrong. Fat supplies much of the taste in food, which leads to satiety, the feeling of being full. In a way, eating fat helps us know we've had enough and it's time to get up from the table. Surprisingly, Helerstein and Taubes agree on another theory: that bad carbs can kill. Taubes contends that carbs cause heart disease, cancer, even Alzheimer's disease. "These diseases cluster together in populations," Taubes said. If you get fat you increase your risk of all these diseases. The obese have a higher risk of Alzheimer's than do the lean. So the natural, simplest possible hypothesis is that what causes one causes all."

Helerstein goes further: "If you are eating sugar, and lots and lots of sugar and pasta and bread and white rice and white grains and white bread and white cereal, then you are initiating, after you eat, an insulin response," she said. "Insulin is an inflammatory hormone and it is a storage hormone. And I don't disagree with him. Where I disagree is, what carbohydrates are you eating? If you're eating the low-sugared, natural carbohydrates, they do not contribute to any degenerative diseases. If you are eating the wrong carbohydrates, I agree with him 100 percent."

Taubes' most controversial theories in the book are these: that there's no evidence saturated fat and cholesterol do anything for us, either positive or negative. They don't cause heart disease, he claims. Nor does salt cause high blood pressure and hypertension. He says fiber is not a necessary part of our diet, especially if we cut out the carbs. And perhaps most controversial of all, Taubes said exercise does not lead to weight loss.

"Exercise makes us hungry," he said, which causes overeating, and leads to the buildup of insulin mentioned earlier. He posits that thin people aren't thin because they exercise, rather, they exercise because being thin gives them the energy to work out.

'Everything in Moderation'

Helerstein said Taubes is wrong about exercise. "I don't think that you have to wake up and exercise for four hours a day," she said. "But the answer to health is really keeping your lean muscle mass strong. And the older we get, the harder that is to do. So each year we lose a little muscle mass, and it's really harder to stay thin and healthy. But I think that again, if a person exercises in moderation and doesn't overdo it, it's a really important factor in health. "

Taubes said he isn't touting any particular diet (though he does say "Atkins was right"). He said he's just trying to get scientists to test the work of the researchers he quotes in his book and see if their theories are correct. But he's expecting a large helping of criticism when the book is released.

"First, they'll shoot the messenger," he said. "And then over the next 10 or 15 years, they'll debate the message and a good portion of it might be accepted. I'd say 70, 80 percent. But you don't thank people for pointing out your mistakes. It's not human nature, in general."

But for most people the bottom line is, our tastebuds and our hearts control what we eat. Raffaele Esposito, owner of the restaurant where we took Taubes to lunch, says pasta is the heart of life. "It's pasta and life," Raffaele said. "You know? If you stopped the heart, you die." Everything in moderation, he said. Everything in moderation.