There is an Obesity Gene (Ob) whose gene product is Leptin

1.Leptin circulates at a level proportional to body fat

2.Leptin enters the nervous system in proportion to its plasma concentration

3.Leptin receptors in brain neurones regulate energy expenditure and energy intake

Leptin is an AFFERENT signal in a negative feedback loop that maintains constancy of Adipose Tissue Mass

Increase LEPTIN promotes a negative Energy Balance when Energy Expenditure > Food Intake

Decrease LEPTIN promotes a positive Energy balance when Food Intake > Energy Expenditure