Honestly, otak-otak is one of the better snacks you can eat if you're watching calories. Eighty calories per piece, 8g protein, and the main ingredient is mackerel, which is real food. The coconut milk adds 18 calories and the aromatics (shallots, chili, lemongrass, belacan) contribute about 13 more, but none of that is crazy. The banana leaf grilling gives it that smoky char without you adding any oil. Compare this to pisang goreng or karipap and otak-otak wins every time, bro.
What actually changes the math is the cooking method and how many pieces you eat, because nobody stops at one. The steamed Nyonya version drops to 65 calories per piece. The recipe typically uses slightly less coconut milk than the grilled version, so the overall fat content is a bit lower. The fried version (otak goreng) jumps to 110 calories from the oil absorbed during shallow frying. That's a 37% increase from doing basically nothing different. If you're buying from a hawker stall and they're selling by the stick, three to four pieces grilled is 240 to 320 calories, decent protein hit of around 24 to 32g, and it won't ruin your day. Five or six pieces starts adding up fast so count before you eat.