Final answer:
Leptin is a hormone that influences food intake and long-term appetite. It is produced by fat cells and regulates the balance between food intake and energy expenditure.
Step-by-step explanation:
Leptin can best be described as a hormone that influences food intake and long-term appetite. It is produced mainly by fat cells and regulates the balance between food intake and energy expenditure. When there is more adipose tissue, more leptin is released, leading to a feeling of fullness and decreased hunger. On the other hand, less fatty tissue means less fat and less leptin, which increases appetite.