Opor is milder than gulai but it is still coconut milk, and that is where the fat comes from. Of the 24g fat in a bowl, roughly half is the chicken skin and half is the santan. A 150g piece of thigh with skin is about 250 calories; the 90ml of gravy it sits in is about 130. If you eat breast without skin and only a spoon of gravy, the same bowl is 260.
The protein is the good part. 34g per serving is high, because the piece is big and it is simmered rather than fried, so nothing is lost to a crust. On a normal day at a warung this is Rp 15,000 to 20,000 with rice, and the meal is about 650 calories, which is a fair trade for that much protein.
Lebaran is when it gets out of hand. Two ketupat (290), opor with the fattiest piece (450), sambal goreng ati (200) and kerupuk (50) is a 1,000 calorie plate, and then the relatives serve it again at the next house. Three houses is 3,000 calories, and that is where the Lebaran kilo comes from. Not the opor, the repetition.
Opor putih (white, no turmeric) and opor kuning (yellow) are the same in calories. The Solo style with thicker santan is about 40 calories heavier per bowl than the thinner Jakarta version.