Curbing Carbohydrates Reduces Liver Fat Faster Than Dieting

Limiting carbohydrates is more effective than cutting calories in people with nonalcoholic fatty liver disease (NAFLD) who want to reduce quickly the amount of fat in their liver, according to a new study.

Researchers at the University of Texas (UT) Southwestern Medical Center (Dallas, USA) designed a study to determine the relative effectiveness of dietary carbohydrate and calorie restriction at reducing hepatic triglycerides in subjects with NAFLD. To do so, 18 subjects (5 men and 13 women) with a mean age of 45 and a body mass index (BMI) of 35 consumed a carbohydrate restricted--less than 20 g/day, the equivalent of a small banana or a half-cup of egg noodles--or calorie restricted (1,200 kcal/day - 1,500 kcal/day) diet for two weeks. Hepatic triglycerides were measured before and after intervention by magnetic resonance spectroscopy (MRS).

The results showed that the mean weight loss was similar between the groups, at around four kilograms. Hepatic triglycerides were reduced by an average 42% in subjects with NAFLD; however, reductions were significantly greater with dietary carbohydrate restriction than with calorie restriction. Dietary fat, carbohydrate, post-treatment plasma ketones, and respiratory quotient were also related to a reduction in liver triglycerides. Aminotransferase and plasma aspartate also decreased significantly with weight loss. The study was published in the May 2011 issue of the American Journal of Clinical Nutrition.

"This is not a long-term study, and I don't think that low-carb diets are fundamentally better than low-fat ones,” said lead author Jeffrey Browning, MD, an assistant professor of internal medicine at UT Southwestern. "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.”

NAFLD is one of the causes of fatty liver changes, involving steatosis that is not a result of excessive alcohol use. It is also related to insulin resistance and the metabolic syndrome, and may respond to treatments originally developed for other insulin-resistant states, like weight loss, metformin, and thiazolidinediones. Nonalcoholic steatohepatitis (NASH) is the most extreme form of NAFLD, and is regarded as a major cause of cirrhosis of the liver of unknown cause.

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University of Texas (UT) Southwestern Medical Center