This is the snack that fools people. It is airy, it is not greasy to the touch, and it feels like nothing. But the batter is flour, sugar, egg, evaporated milk and custard powder, and one sheet carries 70g of carbs. That is the same carb load as a bowl and a half of rice, eaten standing on the pavement in Mong Kok in about 6 minutes.
Sugar is the main driver. A typical batter uses around 30g of sugar per sheet, which is 115 calories before the flour even counts. That is why the outside caramelises and goes crisp. Fat is actually modest at about 8g, which is why it scores better than a Belgian style waffle (格仔餅) with butter, peanut butter and condensed milk, which the same data puts at 440 calories.
The trendy versions are worse. A matcha or chocolate chip sheet adds 40 to 80 calories. Roll it around a scoop of ice cream and you are at 550 or more. The plain original from a cart is the lowest calorie way to eat this, and at 390 it is still a full meal's worth of energy with only 9g of protein.