Low-carbohydrate diets are a common approach for people wanting to lose weight, but as the researchers in the study, funded by the National Institutes of Health, note, little is known about the effects of this approach on the precursors of glucose in the liver or energy production in the liver.
To investigate this, the team from UT Southwestern Medical Center, led by Dr Jeffrey Browning, randomly assigned 14 overweight or obese subjects to follow either a low calorie or a low carbohydrate diet for two weeks. Seven lean subjects were also monitored on a normal diet.
At the end of the two-week period, the researchers used advanced imaging techniques to look at the different methods or biochemical pathways the subjects used to make glucose.
They saw a “dramatic” difference, according to Dr Browning. Those on the low carbohydrate diet were seen to produce more glucose from lactate or amino acids than those on the low calorie diet.
Moreover, those on the low-calorie diet derived around 40 per cent of their energy from glucogen, a polysaccharide derived from carbohydrates and stored in the liver until needed.
The low-carbohydrate group, on the other hand, obtained only 20 per cent of their glucose in this way. To make up the short fall, their livers were seen to burn fat stores.
This finding is significant excess fat in the liver, and especially triglycerides, can lead to nonalcoholic fatty liver disease (NAFLD) – a condition that, according to Browning, could affect as many as one third of all adults in the United States.
The disease is associated with metabolic disorders, such as insulin resistance, diabetes and obesity – and in the worst cases can lead to cirrhosis of the liver, cancer and inflammation.
“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.
Although weight loss was not a primary concern of the study, the researchers also recorded average weight loss of five pounds for the low-calorie dieters during the two week study. Those on the low carbohydrate course lost an average of nine-and-a-half pounds.
The next stage for Dr Browning and his team is to investigate whether changes that occur in liver metabolism as a result of carbohydrate restriction could actually help people already suffering from NAFLD.
Source
Hepatology 2008;48:1487-1496
DOI: 10.1002/hep.22504 “Alterations in hepatic glucose and energy metabolism as a result of calorie and carbohydrate restriction”
Jeffrey D Browning , Brian Weis , Jeannie Davis , Santhosh Satapati , Matthew Merritt , Craig R Malloy , Shawn C Burgess