The vegetables are not the problem. A pile of blanched kangkung, cabbage, long beans, bean sprouts and cucumber, about 150g of it, is 55 calories. You could eat three plates of that and nothing would happen. The problem is what goes on top. A 45g ladle of bumbu kacang is about 150 calories, because peanut sauce is fried peanuts, palm sugar, oil and a splash of coconut milk, and the gado-gado lady grinds it by hand so it is generous.
Then the starch. Most gado-gado comes with lontong or rice, and 60g of lontong is 65 calories. Tahu and tempe goreng add about 60 for a couple of small pieces. Half a boiled egg is 35, a few emping crackers are 25. None of these is big on its own. Together with the sauce they turn a 55 calorie vegetable pile into a 390 calorie plate, and that is the version FatSecret and TKPI agree on within about 20%.
The Rp 15,000 to 20,000 warung plate is honestly one of the better lunches in Jakarta. You get 16g protein from the egg, tofu and tempe, a lot of fibre and volume, and you are full for hours. The one thing to watch is the gado-gado siram at restaurants, where the sauce is poured until the plate is a lake. That version is closer to 550 calories, with 250 of it in the sauce.
For comparison: ketoprak, which is the same idea with bihun and no vegetables to speak of, is about 520 for a plate. Gado-gado wins because half the plate is actual vegetables. This was one of the plates I leaned on while dropping 42kg, because it is the rare street meal where asking for more costs nothing.