Everything “around you” (the environment) and “in you” (genetic makeup including internal biology) controls your appetite. First and foremost, the body’s continuous energy needs drive our appetite because the energy in food is what keeps us alive. Therefore we are internally wired to get hungry as we need more food to keep going. Blood glucose levels, hormones such as leptin (high levels tell you your full) and ghrelin (levels rise as you get hungry) begin to interact to tell you when to start and stop eating. Early human’s struggle for food caused this internal wiring to evolve to point where you eat all you can when you can because you don’t’ know when food will arrive again AND you had to find or chase it. This system evolved very well for our early ancestors as there were virtually no humans overweight. Enter our current environment where tasty food is everywhere and readily available, most of us are forced to sit in order to make a living and combine that with our still existing genetic makeup of eat all you can when you can and you have the perfect recipe for continuous weight gain. Our genes or internal wiring to eat haven’t changed, only our environment, so what we are witnessing is a clash of human biology, established over hundreds of thousands of years of struggling to find food, and our modern environment where we are constantly surrounded by available great tasting foods. Therefore overall, your appetite is driven by need (energy to stay alive) that on a deserted island would work perfectly. Appetite is also affected by your environment, meaning hunger isn’t the only reason you eat and fullness may not stop you in time to keep your weight under control. Everyone, albeit more difficult for some, has control over the latter by paying attention to weight and food intake. When weight goes up eat less, move more or a combination of the 2 until you stabilize at your desired weight.
There is an old saying: “your genes are the loaded gun but your environment pulls the trigger”. In other words control your environment because you because can, meaning no one has to be overweight.