This is the meal that makes volume eating easy in Hong Kong. A 470g bowl for 260 calories is about the same as a single pineapple bun (310), and it takes 15 minutes to get through. Rice congee is mostly water: the rice itself is only about 40g dry per bowl, stretched into nearly half a kilo of food. You feel full for hours on very little.
The toppings are cheap on calories too. Lean pork slivers are around 30g per bowl, roughly 45 calories and 7g of protein. Half a century egg is about 45 calories and another 3g of protein. The whole bowl is only 6g of fat, which is less than one slab of cha chaan teng butter. Compare that to boat congee (300) or pig giblet congee (310) and the century egg version is the lightest of the popular ones.
What ruins it is the side order. Almost everyone gets a yau tiu (fried dough stick) to dip, and one stick is about 270 calories, more than the congee itself. A zha leung (rice roll wrapped around a dough stick) is 450. So the bowl of congee is 260, but the typical congee shop breakfast with dough stick and a milk tea is 640. The congee was never the problem.