Bro, the crab is not the problem. That half a medium mud crab you're eating has about 107g of edible meat, and the meat itself is only 110 calories with a solid 22g of protein. Honestly pretty decent. The problem is the cooking method. Most restaurants deep-fry the crab first before tossing it in the wok, and that step alone dumps roughly 260 calories of oil into your serving. Then the oyster sauce, dark soy, dried shrimp, curry leaves and all that aromatics pile on another 80 or so. You end up at 450 calories for what is honestly not a huge plate of food. And to be straight with you, that number is a ballpark, not gospel, because solid nutritional data for Kam Heong specifically is thin on the ground. Oil absorption varies a lot depending on the cook, so treat 450 as a reasonable middle ground rather than a precise figure.
What actually moves the maths here is how much oil the kitchen uses, and whether you eat the sauce. A restaurant that goes heavy on the wok oil can easily push this to 550 calories per serving. Order flower crab instead of mud crab and you drop to around 350 calories, mostly because the smaller crab absorbs less oil and yields less meat. If you're eating this at a Chinese seafood restaurant with rice, budget the rice separately, about 250 to 280 calories per plate of white rice. The practical tip: eat the crab meat, go easy on spooning extra sauce over your rice, and if you're splitting a whole crab between two people, portion control is basically built in lah.