The beans are cooked in sugar, so each layer arrives sweet before the syrup goes on. 50g of sweetened red beans is about 90 calories and 40g of mung bean paste is 70, and both are mostly starch and sugar with a little plant protein, 7g in the whole glass. Then the seller pours 50ml of coconut milk, which is 90 calories on its own because coconut milk is 18 percent fat. The published breakdown puts 59 percent of the 329 as carbs and 33 percent as fat, which lines up.
It is a drink sized dessert, and that is the issue. A glass of che ba mau is 330, the same as a plate of banh cuon or a bowl of chao ga with extra chicken, and it goes down in 5 minutes on a plastic stool. Che Thai, the other big seller on the cart, is heavier at 370 to 440 per Long Chau because of the jackfruit, longan and extra condensed milk. Che dau xanh is lighter at 200 to 250.
The ice does the visual work. Half the glass is crushed ice, so the actual food is about 150g, and 330 calories in 150g is denser than a banh mi. The coconut milk on top is the lever: ask for it nuoc cot dua and the glass drops to about 280. Extra coconut milk, which a lot of people ask for, takes it to 420. A second glass because the first one felt small is 660.