The human body has more than one kind of fat cells. There are White fat cells and Brown fat. The white fat cells we usually think of fat store energy and the brown fat, burns energy and gives heat.
When you are born you had a spot of brown fat on your back and it helped control your body temperature.
Scientist suspect that there are no Brown fat an a adult, but if they have its not that important. (Might be important to control your body weight. Adults store brown fat in their neck.)
Adipose cells are unicellular organisms.
Overweight people might be overweight because they do not have enough Brown fat from burning energy. Half of the food every meal goes into your Fat cells that’s why you gain weight. Eating more than you need makes store more fat than you need. When you eat less food the you need, doesn’t let your body store fuel later. Without these important nutrients, the body starts to break down muscle tissue for fuel.
Being overweight in humans/animals doesn’t mean its your body weight it means the amount of Adipose cells. Usually obesity means that you are overweight. Losing fat doesn’t make you lose Adipose cells.