They probably use enzymes to breakdown some cellulose into fructose which is sweeter tasting than glucose or convert glucose to fructose, so they could add less

They probably use enzymes to breakdown some cellulose into fructose which is sweeter tasting than glucose or convert glucose to fructose, so they could add less sugar. FTA:"... finding a way to alter the structure of sugar to boost its sweetening power" and then go on to say since it's sweeter they can use 40% less.