Others see the pervasiveness of the inexpensive sweetener as a symbol of the ill effects of government subsidies given to large agribusiness interests like corn growers.

But the most common argument has to do with the rapid rise of obesity in the United States, which began in the 1980s, not long after industrial-grade high-fructose corn syrup was invented. As the amount of the sweetener in the American diet has expanded, so have Americans.

Although the price differential has since dropped by about half, high-fructose corn syrup came on the market as much as 20 percent cheaper than sugar. And it was easier to transport. As a result, the sweetener soon turned up in all kinds of products, including soda, bread, yogurt, frozen foods and spaghetti sauce.

But with sugar newly ascendant, the makers of corn syrup are fighting back. Last fall, the Corn Refiners Association mounted a multimillion-dollar defense, making sure that an advertisement linking to the association’s Web site, sweetsurprise.com, pops up when someone types “sugar” or “high-fructose corn syrup” into some search engines.

In one television advertisement, a mother pours fruit punch into a cup while another scolds her because the punch contains high-fructose corn syrup. When pressed to explain why it is so bad, the complaining mother is portrayed as a speechless fool.

Audrae Erickson, president of the Corn Refiners Association, said consumers were being duped.

“When they discover they are being misled into thinking these new products are healthier, that’s the interesting angle,” Ms. Erickson said in an interview.

Although researchers are looking into the effects of fructose on liver function, insulin production and other possible contributors to excess weight gain, no major studies have made a definitive link between high-fructose corn syrup and poor health. The American Medical Association says that when it comes to obesity, there is no difference between the syrup and sugar.