Dr. Robert Lustig previously argued that sugar is as bad as tobacco or cocaine. Now, he's advocating for a sugar tax in the Guardian based on a new diet study of obese kids.

Lustig and colleagues asked 43 black and Hispanic children, aged 8 to 18—each with symptoms of metabolic syndrome, which can lead to diabetes—about their eating habits and daily calorie intake, then created a nine-day menu with the same number of daily calories.

In each case, researchers limited sugars to 10% of those daily calories, down from an average 28 percent, and substituted with starches, reports the Wall Street Journal.

"Everything got better," Lustig tells Time. Diastolic blood pressure, triglyceride, and LDL cholesterol levels declined, per the New York Times, fasting blood sugar levels dropped 53 percent overall, kids showed less fat in their livers, and some switched from being "insulin resistant" to "insulin sensitive." The reduction of foods with added sugar "reversed virtually every aspect of their metabolic syndrome," says Lustig.

By replacing chicken teriyaki with turkey hot dogs and sweetened yogurt with bagels, "we can turn a child's metabolic health around in 10 days without changing calories and without changing weight." That doesn't mean you or your kids should follow the study diet.

"We gave them crappy food ... processed food—and they still got better … That's the point," Lustig says. Though Lustig and his team told kids to eat more if they found they were losing weight, some lost weight anyway, reports Time.

That's something critics are focusing on, since weight loss can cause metabolic changes. "We can't be completely certain that the changes are fully attributable to changes in sugar intake," one doctor says.

(One study finds sugary drinks kill as many people per year as the flu.)

This article originally appeared on Newser: Reducing Sugar Boosts Kids' Health Within Days

More From Newser