Leptin is a hormone, that is found in the adipose tissue, as it regulates, how much and where body fat is stored.

This hormone is used by bodies to send messages to the brain. As without leptin the brain would not be aware that its body has eaten enough.

Or that its body has stored enough fat. Also, if there is too much leptin in a body, the leptin hormone loses its ability to let the brain know what it needs to know. Then why bodies need to use leptin is to control how much is eaten.

As definitely brains do need to know, that its body is no longer hungry.

Also, another thing that can happen when there is too much leptin in a body is that the body gains weight. Thus, as the leptin hormone loses its effectiveness to maintain its body normal weight the body may then start to become leptin resistant.

So, then the adipose tissue then produces more of the leptin hormone, as this is how a body controls situations like over-eating.