One of the reasons people on low-carbohydrate diets may lose weight is that they reduce their intake of fructose, a type of sugar that can be made into body fat quickly. Fructose is perhaps best known for its presence in the sweetener called high-fructose corn syrup or HFCS, which is typically 55 percent fructose and 45 percent glucose, similar to the mix that can be found in fruits.