Umai is basically Sarawak's version of ceviche, bro. Melanau people have been eating raw fish this way for generations: thin slices of fresh tenggiri or terubok, dressed with calamansi, sliced shallots, chili, and salt. No cooking, no oil, no coconut milk. At 200 calories for a full serving, it is one of the rare hawker dishes where you can eat the whole plate and not regret it later. The 25g of protein is solid too, roughly the same as a medium chicken breast. Fair warning though, these numbers are a genuine ballpark estimate because there is almost no hard nutritional data published for umai specifically, so take the figures as a useful guide rather than gospel.
What actually moves the calorie count is the fish you pick. Tenggiri lands at about 200 calories a serving, which is your standard order. Swap to umai terubok (the shad-family fish, fattier and oilier) and you jump to around 260 calories for the same portion size. Go the other way with umai udang (prawns) and you drop all the way down to about 115 calories since prawns are much leaner than any fish. The condiments change almost nothing. One thing to watch: some stalls add a splash of chili oil or mix in a tiny bit of sugar to balance the acidity, which can quietly add 30 to 50 calories. Ask if you want to keep it clean.