Com tam is a 700 calorie plate and it does not look like one. The rice is the biggest part: com tam plates are generous, 220g of cooked broken rice is 290 calories, and the grains soak up the fish sauce. The chop is a thin cut pork shoulder or rib marinated in sugar, honey, fish sauce and oil, then grilled over charcoal. A 90g chop is 220 once you count the marinade, and a lot of quan serve 120g chops now.
The sides add up quietly. Bi, the shredded pork skin tossed with thinh (toasted rice powder), is 55 for a small handful. Cha trung, the steamed pork and egg loaf, is 80 for a 40g slice. The spoon of mo hanh (scallion oil) on top is 30. The nuoc mam is sweet, about 15g of sugar per bowl if you pour it all, so 40 calories. None of these feel like food, and together they are 200.
The full plate at a proper Saigon com tam quan is suon bi cha op la, with a fried egg, sometimes a second cha, plus the free bowl of canh (clear soup). That is 820 to 900 calories. The published figures range from 627 to 767 for suon bi cha depending on the size of the chop and rice; 700 is a fair middle for what you actually get on the plate.