Leptin has long been considered a beacon of hope in the fight against obesity. This is because the hormone curbs the appetite. However, many overweight people do not have a deficiency, but rather a high level of leptin in the blood. How can this be explained? Learn more about how the effect of leptin and our body weight are related here.
What is leptin?
Leptin is a hormone produced primarily by the fat cells of the body. It plays a role in the feeling of hunger and has therefore been the subject of research for some time. The hormone leptin is a natural appetite suppressant and is produced mainly by fat cells (adipocytes). However, leptin is also produced in bone marrow, skeletal muscle, gastric mucosa, breast skin cells and parts of the brain. If the fat cells are well filled, they send out leptin and convey the signal “We’re full!”. The exact regulation of food intake is still not conclusively understood. The conditions under which leptin leads to weight gain or loss also remain unclear.
The effect of leptin
Leptin exerts its effects through two different docking sites (receptors) in the hypothalamus. This part of the diencephalon is an important control center for the involuntary nervous system (autonomic nervous system) and produces various hormones. After its connection with one type of receptors, leptin leads to the release of other appetite-suppressing hormones, and after its connection with the other type of receptors, it leads to the inhibition of the release of appetite-suppressing hormones. Ultimately, therefore, it curbs our appetite. Through this mechanism, leptin can be seen as an antagonist of the hormone ghrelin, which promotes the feeling of hunger.
Metabolism of leptin
Furthermore, leptin is thought to interact directly with the sugar regulatory hormone insulin. It has been demonstrated that leptin can stimulate glucose utilization (sugar utilization) independently of insulin, even in diabetic patients. Therefore, leptin is considered a potential alternative to insulin therapy in people with type 1 diabetes mellitus. Side effects of insulin would be eliminated. Clinical studies on this topic are expected to provide definite findings. In addition, leptin leads to an increase in blood pressure, an increase in heart rate and a boost in the development of heat in the cells. Another effect of a high leptin level in the blood is said to be the braking of the urge to exercise. So those who have a lot of leptin hormones in their blood also have less desire to exercise.
The role of leptin in weight loss
For some time, leptin was thought to be a potential appetite suppressant in the treatment of obesity. However, it was found that the majority of obese patients had very high levels of the hormone in their blood. The cause is probably leptin resistance, whereby leptin fails to act at its receptors. Although the level of leptin in the blood is high, the brain does not convey a feeling of satiety. Rather, the feeling of hunger persists and food intake continues. Current knowledge suggests that neuronal causes may be responsible for leptin resistance. Some researchers believe to have found the cause of obesity in leptin resistance. However, the exact metabolic processes have not been fully explored, and current knowledge suggests that the development of obesity depends on many factors.
Diet and leptin
Certain foods – especially foods very high in sugar and fat, for example, fried and caramelized foods – cause inflammation in the brain and leptin cannot work. Currently, there is no firm evidence, but one cause of leptin resistance thus seems to be eating behavior. In addition to leptin resistance, there are genetic disorders that can lead to morbid obesity. Mutations of genes that produce proteins for the leptin metabolic pathway disrupt their function. The effect is similar to leptin resistance – affected individuals have an impaired feeling of satiety. However, such genetic defects are rarely the cause of obesity.
Leptin as a drug
Leptin also exists in the form of leptin analogs. These are artificially produced and virtually mimic the action of leptin in the body. In people with congenital fat cell deficiency (lipodystrophy), leptin is prescribed because they cannot produce it themselves.The drug has only been approved for this indication in the USA since 2014. In the European Union, approval was granted in 2018 under “exceptional circumstances”. This means that the benefit of the drug in people with lipodystrophy outweighs the risk and, in addition, that access to sufficient study data was not possible due to the rarity of the disease. The European Medicines Agency is continuously reviewing new incoming data on the effects and side effects of the drug. The drug is administered by the treating physician as an injection into the subcutaneous fatty tissue. The drug is not available in capsule, globule, or tablet form.
Effect against obesity not proven
Due to the described effects, leptin is often traded as a magic bullet against obesity. The idea is that by taking leptin analogues, leptin levels are increased and fat burning is boosted. However, the manufacturer itself points out that leptin has not been shown to cause weight loss. Instead, severe side effects may occur. It is therefore strongly advised not to use a leptin preparation without first consulting a specialist in metabolic diseases (endocrinologist). Also, the scientific evidence to date speaks against the idea that a mere increase in leptin levels automatically leads to a faster feeling of satiety and thus to weight loss.
Side effects of leptin
If leptin is supplied externally, serious side effects may occur. The body can form defense proteins (antibodies) against the hormone, called anti-drug antibodies. This means that the leptin produced by the fat cells can no longer work – the leptin level decreases even further instead of increasing. Furthermore, autoimmune reactions against the liver and kidneys have been described, which can lead to failure of these organs if they progress.
