You can't "deplete" leptin. You can deplete glycogen -- which is what it sounds like you are describing. Carbs (or lack of) are what result in glycogen stores (or lack of).
Leptin is a hormone that is released by fat cells. When you are underfed (dieting) your leptin levels decline. When you are underfed, your glycogen stores are reduced.
You are mixing the two concepts.
Either way, however, the take home message is that cyclical diets are king for keeping leptin levels and glycogen stores as high as possible.