DALLAS — Jan. 20, 2009 —
People on low-carbohydrate diets are more dependent on the oxidation of
fat in the liver for energy than those on a low-calorie diet,
UT Southwestern Medical Center have found in a small clinical study.
The findings, published in the journal
have implications for treating obesity and related diseases such as
diabetes, insulin resistance and nonalcoholic fatty liver disease, said
Dr. Jeffrey Browning, assistant professor in the UT Southwestern Advanced Imaging Research Center and of internal medicine at the medical center.
“Instead of looking at drugs to combat obesity and the diseases that
stem from it, maybe optimizing diet can not only manage and treat these
diseases, but also prevent them,” said Dr. Browning, the study’s lead
Drs. Jeffrey Browning (right) and Shawn Burgess
have found that people on low-carbohydrate diets depend more on the
oxidation of fat in the liver for energy than those on a low-calorie
Although the study was not designed to determine which diet was more
effective for losing weight, the average weight loss for the
low-calorie dieters was about 5 pounds after two weeks, while the
low-carbohydrate dieters lost about 9½ pounds on average.
Glucose, a form of sugar, and fat are both sources of energy that are
metabolized in the liver and used as energy in the body. Glucose can be
formed from lactate, amino acids or glycerol.
In order to determine how diet affects glucose production and
utilization in the liver, the researchers randomly assigned 14 obese or
overweight adults to either a low-carbohydrate or low-calorie diet and
monitored seven lean subjects on a regular diet.
After two weeks, researchers used advanced imaging techniques to
analyze the different methods, or biochemical pathways, the subjects
used to make glucose.
“We saw a dramatic change in where and how the liver was producing glucose, depending on diet,” said Dr. Browning.
Researchers found that participants on a low-carbohydrate diet produced
more glucose from lactate or amino acids than those on a low-calorie
“Understanding how the liver makes glucose under different dietary
conditions may help us better regulate metabolic disorders with diet,”
Dr. Browning said.
The different diets produced other differences in glucose metabolism.
For example, people on a low-calorie diet got about 40 percent of their
glucose from glycogen, which is comes from ingested carbohydrates and
is stored in the liver until the body needs it.
The low-carbohydrate dieters, however, got only 20 percent of their
glucose from glycogen. Instead of dipping into their reserve of
glycogen, these subjects burned liver fat for energy.
The findings are significant because the accumulation of excess fat in
the liver — primarily a form of fat called triglycerides — can result
in nonalcoholic fatty liver disease, or NAFLD. The condition is the
most common form of liver disease in Western countries, and its
incidence is growing. Dr. Browning has previously shown that NAFLD may
affect as many as one-third of U.S. adults. The disease is associated
with metabolic disorders such as insulin resistance, diabetes and
obesity, and it can lead to liver inflammation, cirrhosis and liver
“Energy production is expensive for the liver,” Dr. Browning said. “It
appears that for the people on a low-carbohydrate diet, in order to
meet that expense, their livers have to burn excess fat.”
Results indicate that patients on the low-carbohydrate diet increased fat burning throughout the entire body.
Dr. Browning and his colleagues will next study whether the changes
that occur in liver metabolism as a result of carbohydrate restriction
could help people with nonalcoholic fatty liver disease. Previous
research has shown a correlation between carbohydrate intake and NAFLD.
Other researchers from the Advanced Imaging Research Center involved with the study were Dr. Matthew Merritt, assistant professor of radiology; Dr. Craig Malloy, professor of radiology and internal medicine; and Dr. Shawn Burgess,
assistant professor of pharmacology. Other UT Southwestern researchers
involved were Jeannie Davis, clinical research coordinator; and
Santhosh Satapati, graduate student. A researcher from Texas Tech
University Health Sciences Center also contributed.
The research was funded by the National Institutes of Health and the American Diabetes Association.
Visit http://www.utsouthwestern.org/digestive to learn more about UT Southwestern’s clinical services in digestive disorders, including liver diseases.