Cheng tng is one of the genuinely smart dessert orders. No coconut milk, no fried anything, no glutinous rice. Just a clear broth with barley, longan, gingko and a few dried bits floating around. At 160 calories with almost zero fat, this is about as light as a sweet bowl gets.
The only thing to watch is the sugar level in the syrup. Some stalls go heavy and you can drink it without realising. Ask for less sweet, get the same shiok experience for maybe 110 calories, and walk away feeling like you cheated the system.