Pork belly is 30 to 35 percent fat raw, and thit kho is cooked slowly enough that the fat softens rather than renders out, so you eat all of it. Long Chau's numbers: 100g of lean pork is 145 calories, belly is 260, and the fatty cuts used for kho are up to 394. A com binh dan scoop is 3 cubes, around 100g, at 300 calories once the sauce has gone in. Ask for nac (lean) pieces and the same scoop is 170.
The egg is the part people miscount. Thit kho in the south uses hot vit, duck eggs, at about 130 calories each, against 78 for a chicken egg and 14 for a quail egg. A serving with 2 duck eggs is 590. The sauce is coconut water (Coca Cola at some quan), fish sauce and 20g or so of caramelised sugar for the pot, so 30 to 40 calories per person, but it soaks into the rice and pushes you to eat more of it.
The meal is the problem more than the dish. Thit kho trung at 460, a com binh dan plate of rice at 300 and the free bowl of canh is 800 calories for lunch, and a lot of that is fat, 34g in the pork alone. Over Tet, when the pot sits on the stove for 3 days and people eat from it at every meal alongside banh tet, the 460 becomes 1,400 a day from one dish. That is why everyone comes back from Tet 2kg heavier.