Bun rieu looks lighter than pho because it is a tomato soup, but the broth is where the calories hide. The rieu cua, pounded paddy crab, is simmered with tomato and then finished with annatto seeds fried in oil, which gives the red colour. That oil is 40 to 50 calories a bowl, and the 300ml of broth ends up around 70. The 200g of bun is 220, the biggest chunk.
The toppings vary by quan and each one adds. The crab and egg raft is about 80 calories for a 60g piece. Two cubes of fried tofu are 50. Huyet, the blood cubes, are close to zero. Cha (pork paste) or gio (pork hock) add 60 to 140 depending on which and how many. A basic Hanoi bowl is 400; a Saigon style bun rieu with tofu, cha, hock and a snail or two is 620.
Then there is the mam tom. A teaspoon of fermented shrimp paste stirred into the broth is only 10 calories but it makes you drink every last spoonful, which means all the annatto oil goes in. And the basket of shredded morning glory, banana blossom and perilla that comes with it is free, so at least the volume is on your side.