Two numbers get quoted for this dish and both are right. The Department of Health figure is 438 calories for 289g, which is a modest plate of rice, lean pork leg and a little gravy with no egg. The common street figure is 690, which is what you actually get at a market stall: 220g of rice, 100g of pork including skin and fat, half a braised egg and a generous ladle of gravy. Order nueng ping (skin and fat included) and you are on the 690 plate, not the 438 one.
The skin is where it moves. Pork leg meat alone is about 200 calories per 100g. With the jelly skin and the fat layer attached it is closer to 300. Thai nutrition sites note that leaving out the skin and fat drops a plate from 600 to 800 down to 450 to 550, which matches the components: about 100 calories of skin and fat, another 40 for the half egg.
The gravy matters more than people think. It is the braising liquid reduced with palm sugar and soy, and a stall ladle is 40 to 50g and 50 to 60 calories, plus a lot of sodium. Some stalls sell a khao kha moo piset (special) with extra pork, a whole egg and a few pieces of intestine or sam chan belly, which lands at 850 or more. That is a dinner, not a lunch.