Fructose, a natural sugar found in plants, gives watermelon and apples their sweetness. The sugar in fruit is harmless for most people, but regularly eating food that contains fructose-based sweeteners can be dangerous. Before the mid-1980s, most food manufacturers used sucrose, or table sugar, to sweeten their products, but they gradually switched to high fructose corn syrup, or HFCS, as a less expensive sweetener. Although fructose appears in a wide array of foods, the largest share of it is in soft drinks, processed food and commercially prepared baked goods, according to the U.S. Department of Agriculture.