Diets do not lower Leptin, in fact popular calorie restricted diets places the body in a moderate mode of starvation with the result being the body becoming more efficient at storing fat.
As soon as there is a drastic reduction in calories, the body slows down and starts to conserve fat . Once metabolism slows down to coincide with the reduction of calories, weight loss stops. Frustration sets in, the diet ends, people eat more. That increase signals the end of “survival mode” in the body causing the release of Leptin. And, a primary survival goal of Leptin is to replenish fat storages. A reason dieters gain all the weight back and then some.
Diets or appetite suppressants rely on calorie manipulation, a technique that allows for short term “weight loss” (water and lean muscle loss) and more storage of fat now and in the future. Weight loss is predominantly lean muscle loss, your fat to muscle ratio rises and you have set up your body to become very efficient at storing fat.