Leptin and Leptin Resistance

The body’s metabolism is an extremely complex set of biochemical processes that are regulated by the brain via hormones. The most popular among their ranks are insulin, testosterone, estrogen, adrenaline, and so on. Leptin and ghrelin, however, find themselves ever more in the spotlight as they regulate satiety and hunger, directly affecting body weight. 

What Is the Role of Leptin? 

Discovered just over 20 years ago, leptin is mainly secreted by the cells of  white fat tissue, but is also secreted from the liver, placenta during pregnancy, and more. Its primary role is to signal the hypothalamus in the brain that it has enough energy and energy reserves and does not need more food. Therefore, it is also called a hormone of satiety, and the translation of its name from Greek means "thin, slim". 

Leptin doesn’t just signal the brain when to eat and when not to, it also: 

• Participates significantly in the workings of the body’s metabolism.
• Plays a role in the sexual maturation of teenagers and is crucial to the female reproductive abilities. At a much lower percentage of fatty tissues, the body can not carry a healthy baby to term and extremely low leptin levels are accepted by the brain as a sign to stop ovulation.
• Has a significant role to place in the immune system's stability, and the proper development and formation of bone mass, blood sugar and blood pressure. It is believed to be involved in the processes of blood cell and blood vessel formation.
• Increases thermogenesis and accelerates fat burning, which maintains the body's constant homeostasis, and you enjoy constant weight.
• Remains in balance not only with ghrelin, but also with insulin, cortisol, testosterone, the thyroid hormone, the gonadotrophic hormones, melatonin, etc. Controls other hormones that stimulate the appetite. 

Typically, men have lower levels of leptin and testosterone reduces its production. 

How Leptin Controls Appetite 

Reducing the calorie reserve greatly reduces the amount of the hormone. Leptin receptors register this deficiency and through the hypothalamus, the signal travels to the brain. The brain counts this as hunger and gives a sign that food is needed – the appetite increases. 

While eating, leptin secretion begins to accelerate. Shortly after you finish a meal and the leptin reaches its required level, the receptors in your hypothalamus are activated and you stop feeling hungry. The shorter the period of hunger (decreased energy intake), the faster the normal leptin levels recover and the feeling of satiety appears. 

Why Diets and Starvation Lead to Dubious Results 

When starvation lasts longer, the hormone reaches its normal levels more slowly. You eat more than before until you recover lost fat stores and even accumulate a little more reserve. This is the mechanism of the yo-yo effect in most diets. 

And here comes the main question about leptin. If there are more fatty tissues in the body, then the more the hormone is excreted and the fuller you should feel. Why, then, do you still experience difficult-to-control hunger even when you’ve visibly put on weight? 

It’s Leptin Resistance to Blame 

With the increase in fatty tissues, the amount of leptin produced also increases. The receptors then increasingly become “spoiled” and require larger and larger quantities to activate. Finally, they reach a state where they do not react at all to the already abundant leptin. The absence of signals to the brain registering the hormone means one thing – food is insufficient. What comes next is to be expected. The brain orders the body to eat. You experience a state of constant hunger, overeat, accumulate fat and increase leptin production. Thus, you’re reduced to being “fat and hungry.” 

It is believed that the roots of leptin resistance track back millennia ago. Back then, food abundance occurred only in summer, while people often starved throughout the remaining seasons. That's the reason the body has learned to reduce the alertness of leptin receptors and thus build up reserves for the upcoming times of hunger, during which receptor’s sharpness recovered. 

Over the last several decades, food has been abundant at all times. But your body has no way of knowing it, and it uses food in excess to fatten itself for times of starvation. 

This mechanism, however, makes leptin resistance reversible. How this can be made to happen – read in the next part of the article.