Obese people who consume increased amounts of fructose, a type of sugar that is found in particular in soft drinks and fruit juices, are at risk for nonalcoholic fatty liver disease (NFALD) and more its more severe forms, fatty inflammation and scarring.
Now researchers at Duke University Medical Center believe they better understand what mechanism may account for fructose-related liver injury.
Chronic fructose consumption in a diet puts people at risk for depleting their store of critically important molecules called ATP, which provide liver cells (and other body cells) energy for important cellular processes, including metabolism.
"The stores of liver ATP are decreased in obese and/or diabetic individuals who chronically consume increased amounts of fructose-containing beverages," said lead author Manal Abdelmalek, M.D., MPH, Associate Professor of Gastroenterology & Hepatology at Duke.
The study was published online at the Hepatology journal site on May 2.
Nonalcoholic fatty liver disease is currently the leading cause of chronic liver disease in the United States. This condition can lead to elevated liver enzymes, inflammation and rarely even advanced scarring (cirrhosis) in individuals who do not drink alcohol. In obesity and/or diabetes, the ability of the cells to optimally make ATP may already be impaired.
Unlike other simple sugars, fructose requires ATP for its metabolism. The inability to optimally generate cellular energy as well and the continued consumption of ATP from chronic fructose ingestion can result in the liver's depletion of energy. ATP depletion may increase risk for inflammation and scarring in the liver.
"The state of being insulin resistant impairs the ability of a vital enzyme, AMP kinase, to make new ATP molecules," Abdelmalek explained. "Increased fructose consumption, and excess utilization of ATP favors the increase in molecules that lead to increased fatty acid synthesis as well as increased uric acid."
The researchers also noted that more uric acid is produced in the body when excess fructose is consumed. Too much uric acid is associated with conditions that include gout, high blood pressure, cardiovascular disease, type 2 diabetes, metabolic syndrome and uric acid stones, a form of kidney stones.
The silver lining is that measuring the amount of uric acid in these individuals may help doctors predict the presence and monitor the severity of nonalcoholic fatty liver disease, Abdelmalek said.