In an unexpected discovery, an interdisciplinary team of 21 researchers at Duke University Medical Center has found that excess protein consumption, in addition to high dietary fat intake, may contribute to the development of insulin resistance. Past studies have determined that insulin resistance is linked to obesity.
The study examined the metabolic profiles of 141 individuals. It found that high levels of branched-chain amino acids, which constitute protein, along with high levels of BCAA breakdown products primarily distinguish obese humans from non-obese humans. The impact of increased BCAA intake on insulin resistance was subsequently tested in rats.
The study was funded by GlaxoSmithKline and the National Institutes of Health, appearing in this month's issue of Cell Metabolism.
"What we have been trying to develop at Duke for the past seven years is a platform to allow us to complete a very comprehensive analysis of how metabolism changes in different conditions," said principal investigator Christopher Newgard, Trinity '78 and director of the Sarah W. Stedman Nutrition and Metabolism Center.
The discovery of the BCAA-related metabolic profile signature in obese people was unanticipated, Newgard said.
"To our surprise, in a simple comparison of obese and lean human metabolic profiles, the cluster of metabolites that were at the most discerningly high levels were BCAAs and their catabolites, not lipids and fatty acids as you might expect," he said.
Whereas past studies in metabolomic profiling were "small scale" and tested the effects of one hormone level alone, this study was far more comprehensive, said Jie An, co-author of the study and a research scientist with the department of pharmacology and cancer biology.
Now that the combination of high BCAA levels and high dietary fat intake has been found to lead to insulin resistance in rats, further experimentation can be done on humans, An said.
"At the beginning, you have to have grant money for the project, and you cannot just tell humans what to consume," she said. "But now that we've seen something in animals, we can translate the research back to humans."
Researchers involved in the project said they remain cautious about extrapolating knowledge from this study to human metabolic processes.
"These findings would need to be confirmed in studies with people before any dietary recommendations could be issued," co-author Dr. Laura Svetkey, director of clinical research at the Sarah W. Stedman Nutrition and Metabolism Center, told Duke Medicine News and Communications.
Furthermore, Newgard clarified that the study does not suggest that eating protein is bad.
Amidst mixed public health messages, the study primarily shows that protein may become a player in the processes leading to insulin resistance.
"We're bombarded with the message that there's too much fat and too much sugar in our diets," Newgard said. "In the U.S., we don't have any bias against food groups, and we eat everything. This study shows that extra protein makes an independent contribution."
Get The Chronicle straight to your inbox
Signup for our weekly newsletter. Cancel at any time.