High-fructose corn syrup and sucrose are both compounds that contain the simple sugars fructose and glucose, but there at least two clear differences between them. First, sucrose is composed of equal amounts of the two simple sugars -- it is 50 percent fructose and 50 percent glucose -- but the typical high-fructose corn syrup used in this study features a slightly imbalanced ratio, containing 55 percent fructose and 42 percent glucose. Larger sugar molecules called higher saccharides make up the remaining 3 percent of the sweetener. Second, as a result of the manufacturing process for high-fructose corn syrup, the fructose molecules in the sweetener are free and unbound, ready for absorption and utilization. In contrast, every fructose molecule in sucrose that comes from cane sugar or beet sugar is bound to a corresponding glucose molecule and must go through an extra metabolic step before it can be utilized.

This creates a fascinating puzzle. The rats in the Princeton study became obese by drinking high-fructose corn syrup, but not by drinking sucrose. The critical differences in appetite, metabolism and gene expression that underlie this phenomenon are yet to be discovered, but may relate to the fact that excess fructose is being metabolized to produce fat, while glucose is largely being processed for energy or stored as a carbohydrate, called glycogen, in the liver and muscles.

In the 40 years since the introduction of high-fructose corn syrup as a cost-effective sweetener in the American diet, rates of obesity in the U.S. have skyrocketed, according to the Centers for Disease Control and Prevention. In 1970, around 15 percent of the U.S. population met the definition for obesity; today, roughly one-third of the American adults are considered obese, the CDC reported. High-fructose corn syrup is found in a wide range of foods and beverages, including fruit juice, soda, cereal, bread, yogurt, ketchup and mayonnaise. On average, Americans consume 60 pounds of the sweetener per person every year.

"Our findings lend support to the theory that the excessive consumption of high-fructose corn syrup found in many beverages may be an important factor in the obesity epidemic," Avena said.

The new research complements previous work led by Hoebel and Avena demonstrating that sucrose can be addictive, having effects on the brain similar to some drugs of abuse.

In the future, the team intends to explore how the animals respond to the consumption of high-fructose corn syrup in conjunction with a high-fat diet -- the equivalent of a typical fast-food meal containing a hamburger, fries and soda -- and whether excessive high-fructose corn syrup consumption contributes to the diseases associated with obesity. Another step will be to study how fructose affects brain function in the control of appetite.

Source: Princeton University