Panang looks like the small portion at a curry shop and it is, by weight. The catch is that it is reduced coconut cream rather than coconut milk, so 100g of panang is about 158 calories while 100g of green curry is under 100. A 200g bowl of panang and a 250g bowl of green curry end up at about the same 240 to 320 range, but the panang has far less liquid, so people eat all of it.
It is also the highest protein curry per spoon. Sliced pork or beef is the main ingredient with almost no vegetables, so a 200g bowl has about 20g of protein. That makes it a decent topping over rice if you stop at one ladle. The Thai table has panang at roughly 158 per 100g; a restaurant panang nuea with 150g of beef is nearer 450.
Watch the khao rad gaeng plate. Panang is often paired with a fried egg or with pad pak, and because the panang itself is dry, shops give a generous ladle. A plate of rice with panang and a fried egg is about 690 calories, and it is a small looking plate.