Limiting Carbs, Not Calories, Reduces Liver Fat Faster, Researchers Find
ScienceDaily (Apr. 19, 2011) — Curbing carbohydrates is more effective than cutting calories for individuals who want to quickly reduce the amount of fat in their liver, report UT Southwestern Medical Center researchers.
"What this study tells us is that if your doctor says that you need to reduce the amount of fat in your liver, you can do something within a month," said Dr. Jeffrey Browning, assistant professor of internal medicine at UT Southwestern and the study's lead author.
The results, available online and in an upcoming issue of the American Journal of Clinical Nutrition, could have implications for treating numerous diseases including diabetes, insulin resistance and nonalcoholic fatty liver disease, or NAFLD. The disease, characterized by high levels of triglycerides in the liver, affects as many as one-third of American adults. It can lead to liver inflammation, cirrhosis and liver cancer.
For the study, researchers assigned 18 participants with NAFLD to eat either a low-carbohydrate or a low-calorie diet for 14 days.
The participants assigned to the low-carb diet limited their carbohydrate intake to less than 20 grams a day -- the equivalent of a small banana or a half-cup of egg noodles -- for the first seven days. For the final seven days, they switched to frozen meals prepared by UT Southwestern's Clinical and Translational Research Center (CTRC) kitchen that matched their individual food preferences, carbohydrate intake and energy needs.
Those assigned to the low-calorie diet continued their regular diet and kept a food diary for the four days preceding the study. The CTRC kitchen then used these individual records to prepare all meals during the 14-day study. Researchers limited the total number of calories to roughly 1,200 a day for the female participants and 1,500 a day for the males.
After two weeks, researchers used advanced imaging techniques to analyze the amount of liver fat in each individual. They found that the study participants on the low-carb diet lost more liver fat.
Although the study was not designed to determine which diet was more effective for losing weight, both the low-calorie dieters and the low-carbohydrate dieters lost an average of 10 pounds.
Dr. Browning cautioned that the findings do not explain why participants on the low-carb diet saw a greater reduction in liver fat, and that they should not be extrapolated beyond the two-week period of study.
"This is not a long-term study, and I don't think that low-carb diets are fundamentally better than low-fat ones," he said. "Our approach is likely to be only of short-term benefit because at some point the benefits of weight loss alone trounce any benefits derived from manipulating dietary macronutrients such as calories and carbohydrates.
"Weight loss, regardless of the mechanism, is currently the most effective way to reduce liver fat."
Other UT Southwestern researchers involved in the study were Dr. Shawn Burgess, senior author and assistant professor of pharmacology in the Advanced Imaging Research Center (AIRC); Dr. Jonathan Baker, assistant professor of pathology; Dr. Thomas Rogers, former professor of pathology; Jeannie Davis, clinical research coordinator in the AIRC; and Dr. Santhosh Satapati, postdoctoral researcher in the AIRC.
The National Institutes of Health supported the study.
Aerobic Exercise May Improve Non-Alcoholic Fatty Liver Disease
ScienceDaily (Apr. 13, 2011) — Walking on a treadmill for one hour a day may slow the progression of nonalcoholic fatty liver disease in obese people with prediabetes by jump-starting their metabolism and slowing the oxidative damage wrought by the condition, say researchers at the Cleveland Clinic. A study of 15 obese people with nonalcoholic fatty liver disease revealed that the daily walks not only increase insulin sensitivity, but improve the liver's polyunsaturated lipid index (PUI), which is thought to be a marker of liver health.
The improvements are linked to an increase in the hormone adiponectin, said Jacob M. Haus, PhD, research fellow in the Department of Pathobiology at the Cleveland Clinic's Lerner Research Institute. Adiponectin influences the body's response to insulin and is associated with a reduced risk of heart attack because of its anti-inflammatory properties. But obese people often have low levels of adiponectin. Haus will discuss the team's findings at the Experimental Biology 2011 meeting (EB 2011), being held April 9-13, 2011 at the Walter E. Washington Convention Center in Washington, DC.
Participants in the study walked on a treadmill at 85% of their maximum heart rate for 1 hour per day for 7 consecutive days. Researchers measured the participants' body composition, respiration, insulin sensitivity, and PUIs before and after the 7-day program. The researchers also tested the participants' plasma glucose, insulin and adiponectin, and they gave the participants oral glucose tolerance tests (OGTTs), which measure how quickly glucose is cleared from the blood. During the OGTTs, the researchers isolated mononuclear cells (blood cells that have a round nucleus) from the participants' blood to study whether these cells were producing molecules called reactive oxygen species (ROS). High levels of ROS can result in oxidative damage to tissue.
"When people have prediabetes, their blood glucose will be high after an OGTT. We know that hyperglycemia causes oxidative stress, so we wanted to look at [the participants'] monocytes before and after the OGTT," says Dr. Haus. He notes that before the participants began the walking program, their ROS spiked after their OGTTs.
Cutting Metabolic Risks
At study's end, the participants' PUIs had increased an average of 84%. They also experienced increased insulin sensitivity, increased adiponectin and a decrease in the production of ROS, even after their OGTTs.
"We were able to correlate changes in adiponectin with PUI and the body's resting energy metabolism," says Dr. Haus. "The latter gives us an indication of whether carbohydrate or fat is being metabolized. After exercise, the participants were burning more fat."
Burning more fat is a positive reaction to exercise, one that can defend against oxidative damage and therefore the damage of fatty liver disease.
"Exercise appears to affect the cumulative metabolic risk factors for the progression of nonalcoholic fatty liver disease," says Dr. Haus. "We like to think of exercise as medicine."