Isaw is the cheapest high protein snack on the street and the numbers back it up. Chicken intestine is about 110 calories per 100g cooked with 15g of protein, and after cleaning and boiling a stick carries about 25g of it, so around 30 calories. Then the vendor brushes on the sauce: soy, banana ketchup, sugar and a bit of oil. About 5g clings per stick, 15 calories. Five sticks is 225 calories with 20g of protein, which beats most merienda.
Pork isaw (isaw baboy) is the heavy one. Pork intestine is about 200 calories per 100g cooked because of the fat lining, and the sticks are thicker at about 40g, so 90 calories each. Five pork sticks is 450. Same cart, same sauce, double the number. The vinegar dip (sukang maanghang) is about 5 calories per dunk, so it is free for practical purposes.
The real concern with isaw is not calories but cleaning. A well cleaned intestine is boiled for an hour before grilling. A badly cleaned one gives you a bad night. Pick the cart with a queue. The other thing to watch is the sweet sauce: some vendors dredge the stick through it twice, which doubles the glaze to about 30 calories per stick. Not a big deal on 3 sticks, more noticeable on 10.