Just about everyone admits that eating too much sugar can rot your teeth and expand your waistline. But Dr. Robert Lustig, an expert in childhood obesity at the University of California, San Francisco, believes sugar can be lethal. Lustig says sugar causes heart disease, diabetes, hypertension, and many forms of cancer. "It has nothing to do with the calories. It's a poison by itself," he says. Here, a brief guide:

What is Lustig's argument?
He believes that consuming sugar — both sucrose (beet and cane sugar) and high-fructose corn syrup — is deadly, because the body processes sugar in a uniquely malevolent way. In lab rats and mice, it's been shown that when the liver tries to process a significant quantity of sugar, it converts it to fat. That creates insulin resistance, which is believed to be the underlying cause of heart disease, type 2 diabetes, and, maybe, many kinds of cancer. "In Lustig's view," says Gary Taubes in The New York Times, "sugar should be thought of, like cigarettes and alcohol, as something that's killing us."

What is he basing this on?
The fate of the lab rats, for starters. But there is also "circumstantial evidence" linking sugar to a variety of health problems in humans. Americans' sugar consumption peaked in the early 2000s, coinciding with a big increase in obesity and diabetes. In 1980, 6 million Americans were diabetic, and approximately one in seven were obese — rates that had been steady for decades. By the early 2000s, as sugar consumption peaked, 14 million were diabetic and one in three were obese.

Is this idea a popular one?
Increasingly. A 2009 lecture Lustig gave called "Sugar: The Bitter Truth" has gone viral, with more than 900,000 hits on YouTube thus far and approximately 50,000 new views each month. (Watch it here.) "The number of viewers Lustig has attracted suggests that people are paying attention to his argument," says Taubes.

What's the counterargument?
Ludwig's evidence isn't conclusive, and the studies with mice and rats might not apply to humans. More research is needed, and basic questions remain. "How much of this stuff do we have to eat or drink, and for how long, before it does to us what it does to laboratory rats?" asks Taubes. "And is that amount more than we're already consuming?"

So should I give up sugar?
That's probably not realistic, but most scientists agree that Americans are consuming too much of the sweet stuff and should cut way back. The first step is easy, says Barry Popkin, a professor of global nutrition at the University of North Carolina. Just forgo soda and sugary beverages in favor of water and "lightly sweetened drinks." And government can play a role, too, says New York University nutritition professor Marion Nestle at The Takeaway, with new regulations against industries that push sugar, such as soft drink and juice companies.

Sources: NY Times, The Takeaway, Babble