Starch is not sugar, although it will become glucose after digestion, but because of the existence of "digestion" process, its impact on health is very different from sugar, so it is not sugar.
Syrup is sugar. However, if syrup is used and the sugar content exceeds 0.5%, it cannot be called "sugar-free". Otherwise, professional counterfeiters will be very happy, and they will be relaxed and happy after the holiday.
Sugar alcohol is not sugar. Although they have a certain sweetness, their metabolism in the body is completely different from that of sugar, and they will not raise blood sugar or stimulate insulin secretion. The same sweetness, calories are much lower than sugar. At present, sugar-free moon cakes on the market generally use maltitol or other sugar alcohols instead of sugar. As long as it is not fake, it can be sweet but "sugar-free". However, it should be noted that "sugar-free moon cakes" just have no sugar, which does not mean that they are "healthy moon cakes". Mooncakes still need a lot of fat to taste good. In addition, although sugar alcohol is used instead of sugar, there is still a lot of starch.
Finally, to sum up, compared with the corresponding traditional moon cakes, "sugar-free moon cakes" reduce the adverse effects of sugar on health, but they are still high in fat and starch, far from being healthy. Eating is ok, but enough is enough.