The switch made economic sense and, as Davis notes, "back then, there was no suggestion that high-fructose corn syrup was metabolized differently" than other sugars. More recent research suggests, however, that there may be some unexpected nutritional consequences of using the syrup. "Fructose is absorbed differently" than other sugars, says Bray. "It doesn't register in the body metabolically the same way that glucose does."
For example, consumption of glucose kicks off a cascade of biochemical reactions. It increases production of insulin by the pancreas, which enables sugar in the blood to be transported into cells, where it can be used for energy. It increases production of leptin, a hormone that helps regulate appetite and fat storage, and it suppresses production of another hormone made by the stomach, ghrelin, that helps regulate food intake. It has been theorized that when ghrelin levels drop, as they do after eating carbohydrates composed of glucose, hunger declines.
Fructose is a different story. It "appears to behave more like fat with respect to the hormones involved in body weight regulation," explains Peter Havel, associate professor of nutrition at the University of California, Davis. "Fructose doesn't stimulate insulin secretion. It doesn't increase leptin production or suppress production of ghrelin. That suggests that consuming a lot of fructose, like consuming too much fat, could contribute to weight gain." Whether it actually does do this is not known "because the studies have not been conducted," said Havel.
Another concern is the action of fructose in the liver, where it is converted into the chemical backbone of trigylcerides more efficiently than glucose. Like low-density lipoprotein -- the most damaging form of cholesterol -- elevated levels of trigylcerides are linked to an increased risk of heart disease. A University of Minnesota study published in the American Journal of Clinical Nutrition in 2000 found that in men, but not in women, fructose "produced significantly higher [blood] levels" than did glucose. The researchers, led by J.P Bantle, concluded that "diets high in added fructose may be undesirable, particularly for men."
Other recent research suggests that fructose may alter the magnesium balance in the body. That could, in turn, accelerate bone loss, according to a USDA study published in 2000 in the Journal of the American College of Nutrition.
In November, however, Havel and his colleagues published a review in the American Journal of Clinical Nutrition that examined evidence from multiple studies. They concluded that large quantities of fructose from a variety of sources, including table sugar and high-fructose corn syrup, induce insulin resistance, impair glucose tolerance, produce high levels of insulin, boost a dangerous type of fat in the blood and cause high blood pressure in animals. "The data in humans are less clear," the team noted.
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