Leptin is a hormone secreted from adipocytes. The amount of triglycerides stored within the adipocyte determines the amount of leptin it manufactures. Leptin is an anabolic hormone that has important functions regarding satiety, metabolism, fertility, skeletal system and cardiovascular system and defects in the leptin axis can impair those benefits. I also personally believe that leptin promotes beauty as well.
When the adipocyte is accumulating triglycerides, the adipocyte enlarges and the amount of leptin it produces starts to increase, the leptin then goes on to promote growth and repair. However when the adipocyte is losing its collection of triglycerides, the amount of leptin it makes starts to decrease.
Lipolysis is the release of stored fat into the blood. When the body is undergoing lipolysis (like what you see in low-carb diets, diabetes, or starvation), the amount of free-fatty-acids (FFA) increases and leptin production decreases. The increased level of FFAs then impairs the binding of leptin to the receptor-sites. This is where ''leptin-resistance'' comes from.
Insulin and leptin are strongly linked together and both hormones cannot work without one another. Insulin inhibits lipolysis and promotes the storage of fat inside the adipocyte, which increases the amount of leptin and leptin in turn increases insulin-sensitivity (among many other things). That is what happens in healthy metabolism.
In a person with diabetes or a person undergoing starvation, you have insulin-resistance within the adipocyte, which causes increased lipolysis and fat burning. As the subcutaneous fat stores become depleted, the amount of leptin is reduced and any leptin left in the body becomes resistant because of the high levels of FFAs. Of course this makes sense because leptin being a satiety hormone decreases the amount of food you crave, well if your fat-stores are becoming depleted, leptin decreases and becomes resistant in order to make you really hungry and eat more calories in an attempt to restore you fat-stores, which evolutionarily was beneficial because it meant you could live longer during famines.
It's clear to me now that anything that inhibits lipolysis (carbohydrates, alcohol and acipimox for example) will in turn increase leptin and vice-versa.
Edited by misterE, 05 May 2014 - 02:06 AM.