Dr. Robert Lustig, sitting in his cluttered office in a quiet hall of UCSF's main campus, is sounding glum.

It's a few days before the release of his first book, "Fat Chance" - a scientific and passionate diatribe against processed food in general and sugar in particular - and the reviews so far have been "tepid," he says.

"They don't say I'm wrong. What they say is that the science is thin to support the contentions," Lustig says with a sigh. "The thing is, the science is not thin. The science is very there. But it's a popular book, not a science book."

For the record, the reviews of "Fat Chance," which came out Dec. 27, have been better than tepid. But Lustig, who's been on a crusade against sugar for almost six years, is eager, maybe even impatient, for readers to see his side and take up his cause.

Sugar, he argues, is the major culprit behind the country's explosive obesity rates. Sugar has poisoned the food supply and is altering people's biology, compelling them to eat more and move less. Sugar consumption is not unlike nicotine or alcohol addiction, he says, and kicking the habit - and in turn, reducing the waistlines of Americans - can't be done by sheer individual willpower.

In other words: don't blame the fat for being fat, and don't expect most of them to drop the weight on their own.

"I wrote this book to show there is no doubt as to what actually is happening to us, what occurs scientifically," Lustig said. "It's all out of our control. There's no behavior problem, there's only biochemistry."

Lustig has his share of critics, but his demonization of sugar over the past six years has earned him some small amount of celebrity, too. In 2009, a presentation he gave on sugar was posted to YouTube and has since collected more than 3 million hits - that's a dizzying amount of viewers for what is basically a 90-minute classroom lecture.

Getting the word out

Lustig has published a dozen or so scientific articles against sugar, and he's been interviewed widely by national media. Last summer, he sat down with a newly trim and fit Alec Baldwin for a podcast conversation, in which the actor credited giving up sugar for his 35-pound weight loss.

"The bottom line is, biochemically our current food environment does not work for us," Lustig said on the podcast. "Until we fix it, (we) will continue to be sick. We will continue to die of things like diabetes and heart disease."

Baldwin replied: "I'm getting really depressed, and I want to go have ice cream now. You're really bumming me."

Lustig gets that a lot.

"There's a lot of resistance to what I'm saying," he said in a recent interview. "After all, sugar is fun. Sugar is sweet. And it's easy to be pejorative against the obese and say it's their fault."

Lustig's fight against sugar has developed quickly over the past six years, but it was a long time brewing. He started his career in medicine in 1984, as a pediatric endocrinologist in New York; he came to UCSF in 2001.

Lustig, like pretty much every other pediatrician in the country, had noticed an alarming increase in obesity among his young patients. But it wasn't until 2006, when he was asked to speculate during a medical conference about possible environmental causes behind obesity, that he hit on sugar.

For argument's sake, Lustig suggested that fructose - a simple sugar that is naturally occurring in fruits, but also is being pumped into a huge variety of processed foods for taste and preservation - is an environmental toxin.

"They wouldn't let me off the dais after the talk," Lustig said.

Sugar under fire

Saying that sugar is a major cause of climbing obesity rates in the United States was nothing new. Sugar, especially in the form of the high-fructose corn syrup found in sodas, already had come under attack as a form of empty calories - food with little to no nutritional value that can be easily consumed in large quantities.

But, in the minds of most people, sugar was just a calorie-dense treat - a guilty pleasure. What Lustig suggested, and has since broadcast as a public health disaster in the making, is that sugar is poisonous.

His scientific theory is that sugar in large quantities drives up insulin secretion. Insulin triggers the body to either use sugar as fuel or store it as fat, and Lustig argues that fructose is more likely to end up as fat, especially in the liver.

Plus, insulin blocks a hormone called leptin, which signals to the brain when the body needs more or less energy. A lack of leptin tells the brain that the body doesn't have enough energy, which sets off efforts to increase and preserve fuel. In other words, it makes people want to eat more and move less.

Not all believe

Lustig has his critics, of course, even among people who respect his enthusiasm and believe he has some strong arguments. The main flaw in his points, say both his supporters and his detractors - primarily the food and beverage industries - is that it's hard to believe that sugar is toxic.

Forms of sugar are found naturally in all kinds of healthful foods, including fruits and milk. And humans have a natural proclivity toward sweet foods, which surely serves an evolutionary purpose, some scientists say. Sugar in various forms supplies a quick burst of energy useful for everything from early humans trying to evade predators to modern marathon runners pushing toward the finish line.

There's a giant gap, scientists say, between saying people perhaps are eating too much sugar these days and suggesting that sugar is a toxic substance that's almost solely responsible for a wide variety of physical ills.

"We have to tackle a number of things, and sugar is certainly one of them. There's also all the fat in our diets, and exercise is a huge problem," said Dr. Deepak Srivastava, president of the Bay Area Board of Directors of the American Heart Association, which set limits on recommended daily sugar consumption for the first time three years ago.

It's the hidden sugars

Srivastava said it's important to encourage people to take responsibility for their own behavior. Still, he appreciates Lustig's position and doesn't believe he's wrong or misguided in his attempt to portray sugar as a major public health issue.

Undoubtedly, he said, Americans are consuming too much sugar, and it's not all in sodas and candy bars. Sugar is a main ingredient in many breads, cereals, yogurts and condiments. "It's probably necessary to go to the root of what we're being exposed to," Srivastava said.

It takes a very cautious and educated consumer to avoid the sugared products in a supermarket. And that is at the crux of Lustig's complaints. Even if sugar isn't so dangerous in small quantities, most Americans are overexposed to the food and don't even know it - and certainly they aren't aware how it's affecting their biochemistry.

Therein lies, perhaps, the next stage of Lustig's attack on sugar. He's on sabbatical from UCSF this year to take a yearlong master's education course at UC Hastings College of the Law, where he's learning about public health policy.

A hazardous substance

His main goal, he says, is to get fructose identified as a potentially hazardous substance that should be regulated by government, much as alcohol and tobacco are. He recognizes the battle ahead will be rough. Even relatively small advances on sugar - Richmond's failed soda tax initiative, for example, or New York City Mayor Michael Bloomberg's unpopular restrictions on large beverage sales - have met with outrage.

The book, Lustig said, won't change policy. But it may be his first major volley in what he hopes will become a national war.

"The food industry has complete license to put any amount of sugar in any food it wants to. That's just not OK," Lustig said. "I hope what the book does is open people's eyes to what is actually going on around them."