I found an excellent article on how fat cells work. Here is a paragraph or two from the main article. It is well worth reading.
“A typical young male adult stores about 60,000 to 100,000 calories of energy in body fat cells. What triggers the release of all these stored fatty acids from the fat cell? Simple: When your body needs energy because you’re consuming fewer calories than you are burning (an energy deficit), then your body releases hormones and enzymes that signal your fat cells to release your fat reserves instead of keeping them in storage….
Some people are genetically predisposed to have more fat cells than others and women have more fat cells than men. An infant usually has about 5 – 6 billion fat cells. This number increases during early childhood and puberty, and a healthy adult with normal body composition has about 25 to 30 billion fat cells. A typical overweight adult has around 75 billion fat cells. But in the case of severe obesity, this number can be as high as 250 to 300 billion!”