The meat on sate Padang is actually lean. It is beef, tongue and sometimes tripe or heart, boiled in spiced stock first and then briefly grilled without the coconut or peanut marinade that Javanese sate uses. One skewer is around 24 calories and 2.7g protein. Ten skewers is 240 calories and 27g protein, which is a better ratio than almost any other street meat.
The sauce is the surprise. That thick yellow gravy (or red in the Pariaman style) is the boiling stock thickened with rice flour, so it is starch, not fat. A 100g ladle is about 120 calories. It is poured generously and it is what you mop up with the ketupat, and one ketupat is 145 calories. So the meat is less than half the plate.
At Rp 20,000 to 30,000 for ten sticks in Jakarta or Padang, it is a decent evening meal at 500 calories with 30g protein. The version with two ketupat is 645. The kerupuk kulit (fried cow skin) that some carts add on top is another 90 for one big piece, and it goes soggy in the sauce so you eat it fast.
Sate Padang Panjang (yellow, more turmeric) and Pariaman (red, more chili) are about the same in calories. The Padang Kota version uses a darker, thinner sauce with less flour and comes out about 40 calories lighter per plate.