Peristalsis takes place even when the stomach is empty, and these contractions—sometimes called hunger pangs once they become severe—are believed to be triggered by high concentrations of the ghrelin hormone.
In contrast, the hormones peptide YY and leptin can have an opposite effect on the appetite, causing the sensation of being full.
Ghrelin can be released if blood sugar levels dip too low—a condition called hypoglycemia that can result from long periods without eating.
[6] Older people may feel less violent stomach contractions when they get hungry, but still suffer the secondary effects resulting from low food intake: these include weakness, irritability and decreased concentration.
Prolonged lack of adequate nutrition also causes increased susceptibility to disease and reduced ability for the body to heal.
[9] The hormones insulin and cholecystokinin (CCK) are released from the GI tract during food absorption and act to suppress the feeling of hunger.
[14] The regulation of appetite (the appestat) has been the subject of much research; breakthroughs included the discovery, in 1994, of leptin, a hormone produced by the adipose tissue that appeared to provide negative feedback.
Later studies showed that appetite regulation is an immensely complex process involving the gastrointestinal tract, many hormones, and both the central and autonomic nervous systems.
[20] Hypothalamocortical and hypothalamolimbic projections contribute to the awareness of hunger, and the somatic processes controlled by the hypothalamus include vagal tone (the activity of the parasympathetic autonomic nervous system), stimulation of the thyroid (thyroxine regulates the metabolic rate), the hypothalamic-pituitary-adrenal axis and a large number of other mechanisms.
[21] The nucleus accumbens (NAc) is the area of the brain that coordinates neurotransmitter, opioid and endocannabinoid signals to control feeding behaviour.
The few important signalling molecules inside the NAc shell modulate the motivation to eat and the affective reactions for food.
[22] The hypothalamus senses external stimuli mainly through a number of hormones such as leptin, ghrelin, PYY 3-36, orexin and cholecystokinin; all modify the hypothalamic response.
Systemic mediators, such as tumor necrosis factor-alpha (TNFα), interleukins 1 and 6 and corticotropin-releasing hormone (CRH) influence appetite negatively; this mechanism explains why ill people often eat less.
Leptin, a hormone secreted exclusively by adipose cells in response to an increase in body fat mass, is an important component in the regulation of long term hunger and food intake.
Among people for whom these medications are effective in helping with weight loss, most express that the level of food noise in their mind is noticeably reduced.