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You may want to put down that protein shake -- at least if you're a rat.

New research suggests that diets high in protein spell trouble for rats that already eat a lot of fat: It's easier for them to develop a risk factor for diabetes.

The findings might mean nothing for humans. Even so, they raise questions about protein in the development of diabetes, said the study's lead author, Christopher Newgard, director of the Sarah W. Stedman Nutrition and Metabolism Center at Duke University Medical Center in Durham, N.C.

"We've been hearing for a long time that too much fat and sugar are bad," but now protein enters the picture, too, Newgard said.

"In the context of a poor dietary pattern and overeating, protein could start to make a contribution to the illnesses that obese people suffer from," he added.

Newgard and his colleagues launched the study to gain more insight into the role of protein in the diets of those who eat too much. Americans "eat whatever is put in front of us, and we eat too much of it," he said. "Then you are over-consuming protein, fat and sugar."

The researchers gave extra protein to rats in the form of a few types of amino acids. Human bodies break down proteins and turn them into amino acids that contribute to metabolism, Newgard explained.

The researchers found that the extra protein did not cause problems in rats that were on diets with normal levels of fat, Newgard said.

But protein made a difference to rats on high-fat diets. Those who got extra protein didn't need to eat as much to develop resistance to insulin, a risk factor for diabetes.

The researchers didn't follow the rats to see whether they actually became diabetic because the study lasted for just 10 to 12 weeks. The findings are published in the April issue of Cell Metabolism.

The next step is to figure out a way to study the possible effect of protein in humans. That could be a challenge, however, because researchers would have to tightly control the food that participants eat.

"This would have to be relatively short duration," Newgard said. "You can't put people on diets for long periods of time."

But for now, Newgard said, he "certainly would not recommend increasing protein intake as a mechanism of treating obesity."

"If you have a poor dietary pattern to begin with, when you're eating too much fat and sugar and you're also eating too much protein, that's where the problems unfold," he added.

But Lona Sandon, a spokeswoman for the American Dietetic Association, said the research is too preliminary to produce recommendations for people.

"Most people can get more than adequate protein from eating regular and balanced meals throughout the day that include quality lean protein," added Sandon, an assistant professor of clinical nutrition at the University of Texas Southwestern. "Protein shakes are unnecessary for most populations."

Still, she stressed, it's important to understand someone's lifestyle before giving specific recommendations about protein consumption.

More information

The U.S. Department of Agriculture has more on nutrition.

Author: By Randy Dotinga
HealthDay Reporter

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