This is my experience (n=1) as well. I was a distance swimmer, averaging 10-12 miles / week. Possibly interesting: my focus was on an as-efficient-as-possible-for-my-body-type stroke, and I was NOT aerobic (in the sense of being out of breath) pretty much ever. Being out of breath far from shore is pretty scary.

Anyway, not only did I lose weight, but I could eat anything I wanted. I particularly remember a work party. I was on my third piece of cake. One young lady wanted to know "How do you DO that?" My answer: "two miles a day in the water." I suspect the water being moderately cold had something to do with it as well and the fact that I don't drink soda, and tend more towards savory than sweet.