Protein Might Be a Troublesome Nutrient

April 8 -- TUESDAY, April 7 (HealthDay News) -- 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.