This is the soup you want to be greedy with. The broth is water, tamarind, galangal, a little terasi and palm sugar, and a 200ml ladle of it is under 15 calories. Everything else in the bowl is vegetables. The corn cob piece is the biggest single item at about 30 calories, the young jackfruit is 15, the chayote and long beans together are 10, and the melinjo and raw peanuts are 15 to 20 depending on how many the cook threw in.
Compare that to sayur lodeh, which is the same vegetables in coconut milk at about 160 for the same bowl, or gulai nangka at 200 plus. A warteg will put either in the same size ladle for the same Rp 3,000 to 5,000, and the sayur asem version is half the calories. If you are trying to fill up on volume at a warteg, this is the ladle to ask for twice.
The Sundanese version served with ikan asin, tempe and sambal terasi is where the meal gets its calories, not the soup. A plate of rice at 260, a piece of ikan asin at 80, tempe goreng at 95 and the sayur asem at 80 is a 515 calorie lunch, and the soup is the smallest part of it. The Betawi version with more peanuts and a heavier hand on the palm sugar runs about 100 per bowl.
The one warning is the sugar. Some warungs sweeten sayur asem hard, and a bowl with 2 teaspoons of gula merah in the ladle is 110, not 80. It still does not matter much, but if it tastes like dessert that is why.