The "set point theory" concept is that your body has a stable quantity of fat cells by the time you are an adult. The more weight you carried in your childhood and your teenage years, the more fat cells you will have as an adult. These fat cells then become "fuller" or "thinner" as you gain and lose weight as an adult. The set point is the trigger in these cells that will send a message to your brain saying that your fat cells are getting too thin and that you must eat more. Different people's fat cells will have different set points, and the strength of the message is affected by the number of cells. Thus a person with lots of fat cells and a high set point will battle with a strong desire for food when dieting.