Just as recent science has divided dietary fats into good, bad and really bad categories, some scientists now think different sugars also deserve individual scrutiny.

Most experts agree that Americans eat too much sugar, period. But studies in recent years suggest that a simple sugar called fructose might contribute in unique ways to pre-diabetic conditions, obesity and cardiovascular disease.

Fructose, which makes up about half of table sugar and standard high-fructose corn syrup, is metabolized solely by the liver. The other major simple sugar, glucose, can be used by all organs. Researchers are finding that bombarding the liver with high levels of fructose can produce excess internal fat and elevate levels of uric acid, effects that can contribute to insulin resistance, diabetes and heart disease. Some animal studies also link fructose to reduced sensitivity to leptin, a hormone that signals the body to stop eating.

Not all researchers are convinced that fructose poses a unique threat. But the surge in the United States of Type 2 diabetes, fatty liver disease, kidney stones and other weight-related ailments has led the National Institutes of Health to convene a conference in November that will explore the role of fructose consumption in liver function, obesity and diabetes.

“I think that generally speaking we are moving toward a consensus that fructose is the component of sugar that matters,” said Barry Popkin, a professor of global nutrition at the University of North Carolina who has looked closely at sugar and obesity. In addition to fueling scientific discussion, the new studies have added a wrinkle to the debate pitting high-fructose corn syrup against table sugar. While the U.S. Food and Drug Administration in 1983 declared the sweetener to be safe at levels of up to 55 percent fructose (slightly higher than table sugar’s 50 percent), it has not taken a position on high-fructose corn syrup formulations that contain more.

According to a 2010 study published in the journal Obesity, some of America’s most popular soft drinks (Coke, Pepsi and Sprite) can be formulated with corn sweeteners that are nearly 65 percent fructose.

Fructose is intensely sweet and cheaper than other sugars, so boosting levels in a product could reduce calories and costs while keeping the desired sweetness, said lead author Michael Goran, a professor of preventive medicine and director of the Childhood Obesity Research Center at the University of Southern California.

Beverage industry lobbyists have challenged his findings, saying Goran should have used more sensitive testing methods. Goran said follow-up analyses using those methods on a broader array of food and drinks confirmed the original results.

One maker of high-fructose corn syrup, Decatur, Ga.-based Archer Daniels Midland, has been marketing a product called Cornsweet 90, with 90 percent fructose, for several years. The company recommends it for “reduced calorie beverages, jellies and dressings.”

The FDA said in 1996 that it could not determine the safety of HFCS-90 because it has a “substantially different ratio of glucose to fructose” and ADM provided no safety data on the product. That does not make it illegal, the FDA says, because the submission of safety information on new ingredients is voluntary under federal rules.

The FDA says it doesn’t know how much HFCS-90 or other “fructose dominant” sweeteners may be in the food supply, and neither the American Beverage Association nor the Corn Refiners Association responded to Tribune questions about where and how those sweeteners are used. ADM referred questions to the Corn Refiners Association.