I usually lose 1 to 1 1/2 kg or so per week (2 or 3 lbs) on a high-carb diet.

No rocket science here: if you burn more calories during exercise than you take in from food, you lose weight.

If you're reasonably fit, once you start paddling and get into a groove your body starts using fuel from three sources: muscle glycogen, liver glycogen (including constant replenishinment by snacking), and body fat. You need to replenish the first two to avoid crashing, but most of us can afford to burn lots of body fat without replacing it and without suffering any ill effects.