Appetite is a subjective desire, which, of course, is controlled by the nervous system. Neurophysiologists have long found that the neural center that controls human appetite is located in the hypothalamus. The hypothalamus is located below the front part of the brain stem and weighs about 4 grams. The hypothalamus is divided into three parts: anterior, middle, and posterior. The middle part is the tuberal region, which contains a group of neurons called the ventromedial hypothalamic nucleus. In animal experiments, electrical stimulation of the outer part of this nucleus makes animals feel hungry and eat, which is called the hunger center. Electrical stimulation of the inner part of the ventromedial nucleus makes animals stop eating, which is called the satiety center. After destroying both satiety centers, animals will eat a lot and become obese. At this point, if both hunger centers are destroyed, animals will no longer eat. Therefore, the ventromedial nucleus of the hypothalamus is the appetite center that regulates eating.
Regarding the principle of appetite regulation, there are the following hypotheses: one is the fat regulation theory, which holds that human fat can secrete a hormone called leptin, which acts on the hypothalamus to reduce food intake and promote energy consumption; one is the intestinal peptide regulation theory, which holds that after food enters the gastrointestinal tract, the gastrointestinal tract secretes polypeptide hormones that act on the receptors of brain neurons to produce a feeling of satiety; one is the sugar utilization rate regulation theory, which holds that when the glucose utilization rate of brain neurons is low, animals will feel hungry and eat. By externally injecting 2-deoxyglucose to reduce the glucose utilization rate of brain neurons, animals can be promptly stimulated to eat.
In summary, appetite may be regulated by multiple factors. Humans can also control their appetite through rational thinking. The ancient health preservation doctrine advocates "eating only when hungry and stopping before being full", which is best to eat only 70-80% full. This has important implications for healthy eating.