Wikipedia has a pretty good entry about High Fructose Corn Syrup, and it's health effects implications.
High Fructose corn syrup: Health effects
exerpt
There are indications that soda and sweet drinks provide a greater proportion of daily calories than any other food in the American diet.[20] Overconsumption of sugars has been linked to adverse health effects, and most of these effects are similar for HFCS and sucrose. There is a correlation between the rise of obesity in the U.S. and the use of HFCS for sweetening beverages and foods. The controversy largely comes down to whether this is coincidence or a causal relationship. Some critics of HFCS do not claim that it is any worse than similar quantities of sucrose would be, but rather focus on its prominent role in the overconsumption of sugar; for example, encouraging overconsumption through its low cost.
The possible difference in health effects between sucrose and HFCS could come from the difference in chemical make up between them[citation needed]. HFCS 55 (the type most commonly used in soft drinks) is made up of 55% fructose and 45% glucose. By contrast, sucrose is made up of 50% fructose and 50% glucose. Furthermore, the fructose and glucose in HFCS 55 are in the form of separate molecules; by contrast, the fructose and glucose that are contained in sucrose are joined together to form a single molecule (called a disaccharide). This chemical difference may be less significant in many beverages that are sweetened with sucrose. This is because many beverages are strongly acidic, and the acid in the beverage will cause the sucrose to separate into its component parts of glucose and fructose. The amount of sucrose converted will depend on the temperature the beverage is kept at and the amount of time it is kept at this temperature.
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