The study showed that a low-carbohydrate diet changes hepatic (liver) energy metabolism.
When carbohydrates are restricted, the liver relies more on substances like lactate and amino acids to form glucose, instead of glycerol.
Glycerol are generally used as filler in commercially prepared low-fat foods e.g., cookies.
During the study, the research team led by Jeffery Browning of the University of Texas Southwestern Medical Centre recruited 14 subjects whose BMI fell between 25 and 35, and divided them into two groups of seven, matching them for age, BMI, gender and ethnicity.
They also included seven lean subjects (BMI < 25) to act as a weight-stable comparison group.
They measured the sources of hepatic glucose and TCA cycle flux or citric acid cycle in weight-stable subjects, and in subjects following carbohydrate- or calorie-restricted diets.
The high-BMI groups followed either a low-carbohydrate or a low-calorie diet for fourteen days, while the weight-stable group continued their regular diet.
The low-carbohydrate group was able to maintain hepatic glucose production at the levels observed for the weight-stable and low-calorie groups by increasing glucose formation using lactate or amino acids to match the reduction in glucose formation from glycerol.
In the weight-stable group, who consumed carbohydrates as a significant proportion of their diet, the TCA cycle alone provided sufficient energy to drive glucose formation.
"This was not the case in individuals undergoing carbohydrate restriction," the authors report.
Carbohydrate restriction increased the rate of glucose formed using lactate or amino acids (GNGpep).
"This suggests that in fasted human subjects undergoing weight loss, the elevated gluconeogenesis associated with carbohydrate restriction is driven by substrates such as lactate or amino acids," the authors report.
"We have shown that the sources from which endogenous glucose is produced are dependent upon dietary macronutrient composition," they added.
The researchers suggest that the shift in glucose metabolism associated with a low carbohydrate diet could be beneficial in individuals with non-alcoholic fatty liver disease (NAFLD) due to improved disposal of hepatic fat.
These findings are in the November issue of Hepatology.