The function and properties of leptin have been discussed extensively and few people have thoroughly examined its exact relation to our body and the mechanisms it employs.
What is leptin?
Leptin is an adipokine released by adipocytes; in a simple language, a hormone produced by fat cells. It decreases food consumption, stimulates the process of thermogenesis, improves lipid oxidation and increases insulin sensitivity in cells in the peripheral organs.
Besides monitoring and controlling the long-term balance of energy, it has the potential to affect the activity of neurons. It’s a messenger that goes to your brain and practically notifies it that the current energy levels are sufficient to do the daily essential metabolic functions.
Basically, the brain comes to a conclusion that you can expend energy at a normal pace and not feel tired or drained out.
What is the function of Leptin ?
Let’s observe what happens in your body when leptin go down. If the leptin levels are reduced, the brain will look at this as if you were in a situation where you are starving.
What happens is that if the brain doesn’t get the “message” from leptin that there’s enough energy, the brain will start thinking that you are starving making you go into “couch potato” mode, so that it can prevent you from burning any additional reserves of energy.
The brain will get “scared” thinking “I shouldn’t waste energy needlessly and need to preserve as much as possible since I don’t know when’s the next time we’ll find food”. The body will react by suppressing the metabolism in order to conserve calories as much as possible.
This is a natural occurrence during pregnancy and puberty. This may sound odd at first and you might be wondering what is it that connects these two conditions. Well, looking from another perspective, if leptin were always active, it’d be really difficult to gain any amount of weight.
Leptin, weight gain and weight loss
If women couldn’t gain weight during pregnancy, we wouldn’t have been able to survive as a species. Looking at it from the point of Darwin’s theory of evolution and “survival of the fittest” if we can’t gain weight and preserve energy we won’t be “fit” to survive and propagate our genes which would lead to the extinction of our genes.
And what happens with those who still haven’t gone through puberty or those who passed it? What about those who aren’t pregnant? Why do they experience it too?
The thing is that leptin signals to the hypothalamus that there’s enough energy left to burn. If the hypothalamus gets the message from leptin, the body enter a state of anorexigenesis, which is basically appetite loss. This basically means that the brain gets the message that it isn’t hungry and that it has the permission to use fat deposits as an energy source.
The aforementioned process triggers the sympathetic nervous system resulting in a surge of energy which will cause the fat cells to release the stored fat. Additionally, anorexigenesis notifies the vagus nerve, also called the energy storing nerve to cease insulin release since the body isn’t hungry. If in this instance, the hypothalamus doesn’t get the leptin message, the body gets into a state of orexigenesis, which means gaining an appetite.
This, in turn, means that the brain will get the message that the body is starving and tell it to preserve energy. This causes the sympathetic nervous system to turn off, so to speak. When this happens, the vagus nerve “turns on”. Then, the brain thinks that the body is hungry and needs more leptin. When it needs leptin, the body releases a larger amount of insulin.
How does leptin work in relation to fat loss ?
Now, let’s examine the two different ways in which the body reacts when it gets the leptin signal and when it doesn’t. Let’s say you had a soft drink. The sugar in it starts filling up your fat cells.
Once they’re filled, the brain gets the message and the SNS is then increased. What happens then is that you get an energy spike also known as having a “sugar-high”. Your brain looks at this as an opportunity to expend energy by using your fat deposits as an extra available energy.
What is Leptin resistance ?
We concluded thus far that releasing leptin stimulates the sympathetic nervous system. If the brain can’t get the leptin message, it assumes it’s hungry, forcing it to slow down on most of the metabolic processes in order to preserve energy.
Even in the previous example of drinking a soft drink or a soda, if that person is leptin resistant, their body doesn’t realize it’s just ingested food. This leaves the person hungry and trying to eat more food in the effort to get the brain off of thinking that they are starving. Nutritional scientists have concluded that overweight people release bigger amounts of leptin in comparison to lean people.
What they found was that overweight people regularly experience high levels of leptin and have an ineffective response mechanism to it. This is usually known as being “leptin resistant”, that is related to the ineffective transport of leptin through the brain-blood barrier.
This results in decreased leptin signaling to the hypothalamus and increased food consumption and fat gain in the liver and adipose tissues.
What this means is that that the leptin molecules aren’t binding with the receptors in the brain that tells your brain to require more food (the reason why plasma levels are increased).
That’s why it is essential that you incorporate regular re-feeds in your diet. This will provide many positive psychological benefits, as well as boost your metabolism.