Leptin Resistance and Obesity

Leptin resistance is currently a big area of research in the field of obesity treatment. As you may know, leptin is a hormone that through interactions with the brain or other areas of your body cause many things to change: appetite, metabolic rate, fat burning hormones, etc.

So how does this interaction occur? Well, it occurs in the same way that all interactions occur – through receptors. In general, each hormone can bind only to a specific receptor, and for this reason the usual analogy is a key that opens a specific look.

Therefore, leptin receptors will bind only leptin and not insulin or any other hormones.

Subsequently, different reactions occur according to the particular area where the receptor is located. For instance, when binding a receptor in pancreas, leptin will influence insulin secretion. In muscle cells, leptin will influence glycogen storage, and so on.

However, leptin can't reach the brain like the other tissues because it has to cross something called blood brain barrier. This BBB exists to protect your brain from substances that are not supposed to get there. (Fatty acids cannot be used to provide energy for the same reason.)

In this case, leptin needs a certain transporter to get across this barrier. And if you guessed that having a transporter problem causes resistance to this hormone, you are right.

It is believed that when too much leptin is floating around, this transporter can become saturated, which would impair its normal functioning. Therefore, leptin transport through the BBB would be more difficult.

It should be noted that most of the time, the resistance is due to lazy receptors. In other words, leptin can cross the BBB without any problem, but the receptors are resistant or don't work very well.

So more leptin is necessary because the brain doesn't respond properly to its signal. This is very similar to what happens in insulin resistance, when chronically high levels of hormone secretion cause the receptor to become even more resistant over time.

Gradually, leptin resistance will lead inevitably to fat gain. This happens because your brain has a sort of preconceived notion of how fat it wants you to be, and having more and more leptin will push upwards this set point.

So this is a vicious circle: you get fatter then more leptin is secreted, then you get fatter, and so on. Not a nice picture...

The research shows that this resistance is partly genetic and partly environmental. Most people are born with it, so they are more prone to get fat. Moreover, their crappy nutrition habits and lack of exercise usually accentuate this condition.

Their brains will determine a higher set point for leptin, and weight loss will become even more difficult. And when they get at the end of their greasy rope, and finally reduce calorie intake, guess what... Leptin drops, and they go into starvation mode even with lots of body fat available.

In other words, their bodies respond much sooner by slowing their metabolic rate and fat burning, increasing appetite, etc. Which may explain why is so difficult for obese people to lose fat.

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