Leptin
A hormone produced by fat cells that tells the brain about the body's energy reserves and regulates appetite and satiety.
Leptin is the « satiety hormone ». Secreted by adipose tissue (fat), it informs the hypothalamus (brain) about the state of the reserves: more fat = more leptin = « we have enough reserves, reduce appetite ». It is an energy thermostat.
An original angle (leptin resistance): a major paradox: people with obesity have a lot of leptin (proportional to fat mass), but the brain no longer responds to it. This is leptin resistance, comparable to insulin resistance. The brain « believes » it is starving despite huge reserves, so it keeps appetite up and slows metabolism, a vicious circle that traps people in obesity.
Causes of leptin resistance: chronic inflammation, excess fructose (which disrupts leptin signalling), high triglycerides (which block leptin’s passage to the brain), lack of sleep.
The role of sleep (crucial and little known): sleep deprivation lowers leptin (satiety) and raises ghrelin (hunger). The result: after a bad night you are hungrier, especially for sweet and fatty foods. This is a powerful and underestimated driver of weight gain: sleeping too little sabotages appetite regulation.
To improve leptin sensitivity: cut back on fructose and ultra-processed foods, sleep enough, reduce inflammation, be physically active. There is no effective « leptin supplement »; it is sensitivity that needs restoring.