Leptin

Leptin is a hormone produced by fat tissue that acts as a gauge for the body's energy stores and is one of the most important hunger hormones. The more fat tissue the body has, the more leptin is secreted into the bloodstream. Leptin travels via the blood to the brain's hypothalamus, where it signals: 'Energy stores are sufficient - you can expend energy normally, hunger doesn't need to increase, and metabolism doesn't need to slow down.' This system evolved to protect humans from starvation - at a time when food was not continuously available.

Leptin works together with another key hunger hormone, ghrelin. While leptin signals satiety and energy sufficiency, ghrelin is the 'hunger hormone' that rises before meals and increases appetite. The balance of these two hormones significantly regulates how hungry we feel, how much we eat, and how efficiently our body expends energy. In a healthy situation, leptin and ghrelin keep weight stable long-term - but this system can become disrupted.

In the context of weight loss, leptin is a critical hormone to understand. When fat tissue decreases, leptin levels drop - in studies by as much as 50% in the first months. The brain interprets this drop as a threat, as if the body were in danger of starving, and activates strong countermeasures: hunger increases significantly, energy expenditure decreases (NEAT or daily activity unconsciously decreases by 200-400 kcal/day), pleasure from food increases (especially energy-dense foods become more appealing), exercise motivation weakens, and body temperature may drop. This explains why weight loss feels easy at the beginning but becomes significantly harder over weeks and months. It's also one of the biggest biological reasons why lost weight easily returns.

Leptin resistance is a condition where the brain doesn't respond to the leptin signal normally, even though there is plenty of fat tissue and leptin. This is very common in overweight and obese individuals. The mechanism resembles insulin resistance: when leptin levels are consistently high, the brain's receptors become 'desensitized' to the signal. In practice, this means that even though the body has abundant energy stores, the brain doesn't receive the message - and hunger remains high. An overweight person can therefore feel the same biological hunger as an undernourished person, making weight loss exceptionally difficult.

Behind leptin resistance are several mechanisms: 1) Chronic inflammation - visceral fat produces inflammatory markers that interfere with leptin's transport across the blood-brain barrier. 2) High triglyceride levels - triglycerides prevent leptin from reaching the brain. 3) Hypothalamic stress - continuously high leptin levels overload the brain's signal processing. The good news is that leptin resistance is a reversible condition.

Leptin sensitivity can be improved through several concrete methods: 1) Moderate weight loss pace - at most 0.5-1% of body weight per week, so the leptin drop isn't too steep. 2) Sufficient sleep (7-9 hours) - sleep deprivation lowers leptin and raises ghrelin, increasing hunger by up to 24% the following day. In studies, even one bad night significantly altered hormonal hunger. 3) Stress management - cortisol interferes with leptin function and increases hunger especially for energy-dense foods. 4) Periodic maintenance phases during weight loss (1-2 weeks of eating at maintenance calories) allow leptin to recover and reduce the body's countermeasures. 5) 'Refeed days' - temporary increases in energy and carbohydrates (10-15% above maintenance calories, primarily from carbohydrates) can temporarily raise leptin and ease hunger. Carbohydrates raise leptin more effectively than fat or protein. 6) Exercise - regular exercise improves leptin sensitivity by reducing inflammation and improving insulin sensitivity. 7) Reducing inflammation - omega-3 fatty acids, antioxidant-rich foods, and reducing processed foods support leptin sensitivity.

It's important to understand that leptin supplements don't work for weight loss. Because the problem with leptin resistance is in the brain's reception - not a lack of leptin - additional leptin doesn't help. Externally administered leptin also doesn't survive the digestive tract, so oral supplements are ineffective.

Leptin is closely related to ghrelin, cortisol, calorie deficit, and yo-yo dieting concepts. By understanding how leptin and other hunger hormones work, you can make weight loss more sustainable and avoid the most common biological pitfalls.

Last updated: March 30, 2026