The findings controlled for obesity, physical activity, and a number of economic and social variables.

New York Times columnist Mark Bittman called the new study "the closest thing to causation and a smoking gun that we will see" for the relationship between sugar and diabetes.

But not everyone agrees this paper is the "smoking gun" for sugar.

Frank Hu, an expert on diabetes epidemiology at Harvard, tells The Salt that while the study's findings track with other research linking sugar intake to the diabetes epidemic, Lustig's study by itself is "weak evidence of a causal link."

Why? Because, he says, epidemiologists don't consider ecological studies like this one, which take a statistical snapshot, as reliable as prospective cohort studies, which follow a group of people over time.

Hu notes that he was also surprised to see that other foods did not predict diabetes risk nearly as strongly as sugar in Lustig's study. "I don't know why this happened, because we know other foods are associated with diabetes risk – like highly refined grain products, white rice, bread, and other starchy foods. Those foods are not very different from sugar. But maybe sugar is a better indicator of certain dietary habits of population."

Lustig himself is the first one to admit that proving that any one thing causes a disease, especially a chronic disease, is tricky business. And Lustig's co-author Sanjay Basu admitted on an epidemiology blog this week that "we can't 'prove causality' through any amount of statistics."

But Lustig insists that nailing down sugar's role in the rise of obesity and diabetes is useful, because it will give people a starting point.

"The point is, if [diabetes is caused by] many things, you can handle each one, one at a time," says Lustig.

Where to start, then? Well, Lustig says, we could start by regulating it better, with stricter guidelines for sugar consumption, and taxes on it.

Sounds like he'll soon be pushing for legislation — especially since the doctor is pursuing a law degree.

He's certainly no lightweight when it comes to getting out the message. His YouTube video "Sugar: The Bitter Truth" has attracted millions of viewers since it went viral in 2010.

Copyright 2013 NPR.

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Sugar's Role In Rise Of Diabetes Gets Clearer