Fructose is found naturally in fruits and vegetable, but it's also found in many sugars, from cane and beet to high-fructose corn syrup. Dr. Lustig says excessive amounts of dietary fructose is a problem and it doesn't matter if the sugar comes out of the ground or is made in a factory. He points out sugars and sweeteners used in processed foods are half fructose, and it's the fructose which is the problem.