I've began taking protein powder, why am i losing weight?

I'm curious to know. I ama distance runner and also a vegetarian I lift weights 4x a week. I always wanted to lose a few points to cut a bit of time off and also get really cut. Recently i began taking this vegan protein powder, i instantly saw improvements in my performance and I began to see more defined muscles especially in my abdominal. I never used to see results from my weight lifting and core trainign, but its relly starting to show now,. ive also dropped a size. Why is protein powder so effective?