When the waiter asks 紅湯定白湯 (red soup or white soup), red is the right answer every time. Borscht is about 90 calories a bowl and cream of mushroom is 170. The cream soups are made with roux and evaporated milk, so a bowl carries 11g or more of fat. Borscht is tomato, cabbage and stock with almost no fat, about 2.5g. Choosing red over white every workday saves around 400 calories a week without changing anything else you eat.
The soup is mostly vegetables and water, which is why the number is low. A bowl has maybe 15g of beef, 60g of cabbage, potato and carrot, and 170ml of tomato stock. The tomato paste and a bit of sugar give it around 12g of carbs. This is the closest thing to a volume food on a cha chaan teng menu: 250ml of hot food for 90 calories that takes the edge off before the main plate arrives.
The catch is salt. The same nutrition service put the sodium at around 1,000mg per bowl, and a dietitian estimate elsewhere puts some cha chaan teng versions near 1,950mg, which is a full day's worth. Restaurants boost the flavour with tomato paste, stock cubes and salt because the vegetables are cheap and bland. So the calories are fine; the sodium is not, and a person watching blood pressure should treat it as a few spoonfuls rather than a bowl to finish.