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.