University of Illinois researchers say that dietary fructose affects a wide range of genes in the liver that had not previously been identified, and thus ingesting too much of it may be harmful.
Lead author Manabu Nakamura highlights the fact that most people consume quite a bit of fructose in the form of table sugar and corn syrup, which is used in products as diverse as soft drinks, protein bars, and fruit juice.
He further says that many scientists are of the view that high dietary fructose may lead to metabolic syndrome, a group of risk factors that predict heart disease and Type 2 diabetes.
"For this reason, it's important for scientists to understand exactly how consuming high amounts of fructose affects human health," said Nakamura, an associate professor of Food Science and Human Nutrition.
With an eye on making recommendations about its dietary use, he and his colleagues are continuing to study the metabolism of fructose.
Nakamura says that his study goes to indicate that the metabolism of fructose is more complex than the data had indicated.
"Our gene-expression analysis showed that both insulin-responsive and insulin-repressive genes are induced during this process. Our bodies can do this, but it's complicated, and we may pay a price for it," he said.
According to him, the body handles most carbohydrates fairly simply-converting them quickly to glucose, and using them for energy or storing as fat.
"When we are eating, blood sugar-and insulin production-goes up. When we sleep or fast, it goes down," he said.
However, the researcher adds, the process is not so straightforward with fructose.
"In order for fructose to be metabolised, the body has to create both fasted and fed conditions. The liver is really busy when you eat a lot of fructose," the researcher said.
Since fructose metabolism happens mainly in the liver, the researchers wanted to gain a complete picture of gene expression in the organ during the process.
For their study, Nakamura and his colleagues fed 24 rats either a 63 percent glucose or fructose diet four hours a day for two weeks.
Half the animals fasted for 24 hours at the end of this period, and before the researchers performed a gene expression analysis. The other half were examined at the end of a four-hour feeding.
The researchers observed that fructose feeding induced a broader range of genes than had previously been identified, and that there were simultaneous increases in glycogen (stored glucose) and triglycerides in the liver.
"To our surprise, a key regulatory enzyme involved in the breakdown of glucose was about two times higher in the fructose-fed group than in the glucose-fed group," Nakamura said.
Based on their observations, the researchers said that their findigns suggested that a protein, called carbohydrate response element binding protein, was responsible for the fructose effect on certain genes that trigger the production of fat.
"We're continuing to assess the risk of fructose insulin resistance and the consequent risk for development of diabetes," he said.