Many people falsely believe that weight gain (and loss) has to do with calories and willpower.
However, modern research on obesity does not agree … and scientists are increasingly targeting a hormone called leptin (1).
Being resistant to the effects of this hormone (called leptin resistance) is now believed to be the Leader Driver of the increase of fat in humans (2).
In the previous video, Dr. Stephan Guyenet, obesity researcher and blogger, explains everything you need to know about leptin and its involvement in obesity.
Meet leptin: the "master" hormone that regulates body weight
Leptin is a hormone produced by the body's fat cells (3).
It is often referred to as the "satiety hormone" or the "hunger hormone".
The main objective of leptin is in the brain, particularly in an area called the hypothalamus.
Leptin is supposed Tell the brain that we have enough stored fat, that we do not need to eat and that we can burn calories at a normal speed (4).
It also has many other functions related to fertility, immunity, brain function and others (5).
However, leptin principal paper is the long-term regulation of the energy balance … the amount of calories we eat and spend, and the amount of fat we store in our bodies (6).
The leptin system evolved to prevent us from starving or eating excessively, which would have made us less likely to survive in the natural environment.
These days, leptin is very effective in preventing us from starving. But something breaks in the mechanism that is supposed to prevent us from overeating.
Bottom line: Leptin is a hormone produced by fat cells in the body. Its main function is to regulate the amount of calories we eat and burn, as well as the amount of fat we carry in our body.
Leptin is supposed to tell the brain that we do not need to eat
The way leptin works is relatively simple …
This hormone is produced by the body's fat cells. The more body fat they carry, the more leptin they produce (7).
Leptin is transported by the bloodstream to the brain, where it sends a signal to the hypothalamus … the area of the brain that controls when and how much we eat (8).
Fat cells use leptin to "tell" the brain how much body fat they carry. A lot of leptin tells the brain that we have a lot of stored fat, while low levels of leptin tell the brain that fat stores are low and that we are at risk of starvation (9).
This diagram shows how leptin is supposed to work:
We eat -> increases body fat -> increases leptin -> we eat less and burn more.
We do not eat -> low body fat -> low leptin -> we eat more and burn less.
This type of system is known as a negative feedback loop and is similar to the control mechanisms for many different physiological functions … such as breathing, body temperature, blood pressure and others.
Bottom line: The main function of leptin is to send a signal to the brain, "tell" how much fat is stored in the fat cells of the body.
Resistance to leptin may be the main biological abnormality in obesity
Obese people have a lot of body fat in their fat cells.
Because fat cells produce leptin in proportion to their size, obese people also have very high levels of leptin (10).
Given the way leptin is supposed to work, these people should not be eating … their brain should to know Have a lot of stored energy.
However … the problem is that the leptin signal is not working. There is a whole ton of leptin floating around, but the brain does not "see" it is there (11).
This condition is known as leptin resistance. Now it is believed that it is The main biological anomaly in human obesity. (12)
When the brain does not receive the leptin signal, it erroneously thinks that the body is starving, even though it has more than enough stored energy.
This causes the brain to change our physiology and behavior to recover the fat that the brain thinks we are losing (13, 14, 15):
- Eating more The brain thinks we MUST eat so that we do not starve.
- Reduction of energy expenditure: The brain thinks that we need to save energy, so it makes us feel more lazy and burns us less calories at rest.
In this way … eating more and exercising less is not what why of weight gain, is the consequence From resistance to leptin, a hormonal defect (16).
For the vast majority of people, trying to exercise cognitive inhibition (will power) on the signal of starvation driven by leptin is almost impossible.
Bottom line: Obese people have high levels of leptin, but the leptin signal is not working due to a condition known as leptin resistance. Resistance to leptin can cause hunger and reduce energy expenditure.
Losing weight reduces leptin, so the brain tries to regain weight
Most "diets" do not provide good long-term results. This is a well-known problem in weight loss studies.
Diets are so ineffective that every time someone goes from being obese to thin, it is considered a material of journalistic interest.
The truth is … when it comes to losing weight, long-term success is the exception, NOT the rule.
There are many possible reasons for this, but research shows that leptin may have a lot to do with this (17, 18).
Losing weight reduces fat mass, which leads to a significant reduction in leptin levels, but the brain does not necessarily reverse its resistance to leptin.
When leptin decreases, this causes hunger, increased appetite, decreased motivation to exercise and decreased the number of calories burned at rest (19, 20).
Basically, the reduction of leptin makes the brain think that it is starving … so it starts all kinds of powerful mechanisms to recover that lost body fat, mistakenly thinking that it protects us from starvation.
In other words, the active brain. defend the greatest amount of fat mass, using strong biochemical forces that force us to recover lost weight.
Most dieters will be familiar with this … weight loss is often easy at first, especially when the motivation is high, but very soon hunger, cravings and a reduced desire for exercise begin.
This is the main reason why the diet of many "yo-yo" people … lose a significant amount of weight, only to recover it (and something else).
Bottom line: When people lose fat, leptin levels decrease significantly. The brain interprets this as a sign of hunger, changing our biology and behavior to make us recover the lost fat.
What causes resistance to leptin?
According to Dr. Guyenet, several cellular mechanisms behind leptin resistance have been identified.
These include (21, 22):
- Inflammation: Inflammatory signaling in the hypothalamus is probably an important cause of leptin resistance in both animals and humans.
- Free fatty acids: Having high free fatty acids in the bloodstream can increase the metabolites of fats in the brain and interfere with leptin signaling.
- Have high leptin: Having high levels of leptin in the first place seems to cause resistance to leptin.
Quite everyone of these factors increases in obesity … so this can form a vicious circle where people become fatter and more and more resistant to leptin over time.
Bottom line: Possible causes of leptin resistance include inflammation, elevated free fatty acids and high leptin levels. All three increase in obesity.
What science knows about the reversal of leptin resistance
The best way to know if you are resistant to leptin, is to look in the mirror.
If you have a large amount of body fat, especially in the belly area, you are almost certainly resistant to leptin.
A key to preventing (or reversing) resistance to leptin is to reduce the inflammation induced by the diet.
There are several things you can do:
- Avoid processed foods: Highly processed foods can compromise the integrity of the intestine and promote inflammation (23).
- Eat soluble fiber: Eating soluble fiber can help improve intestinal health and protect against obesity (24).
- Exercise: Physical activity can help reverse resistance to leptin (25).
- Sleep: Lack of sleep has been linked to problems with leptin (26).
- Lower your triglycerides: Having high levels of triglycerides in the blood can prevent the transport of leptin from the blood to the brain (27). The best way to reduce triglycerides is to reduce carbohydrate intake (28).
- Eat protein: Eating a lot of protein can cause automatic weight loss. There are many reasons for this, one of which may be an improvement in leptin sensitivity (29).
Are any of these familiar? These are many of the same things that we generally associate with good health.
Unfortunately, there is no simple way to do this. Eat real food, maintain good intestinal health, exercise, sleep well, etc … these are all the efforts of a lifetime that require a drastic change in lifestyle.
Bring the message home
Obesity is not caused by greed, laziness or lack of willpower.
There are strong biochemical forces at play … that are driven primarily by changes in the environment, and in particular in the Western diet.
The truth is… everywhere This diet continues, obesity and chronic disease continue.
Not because this diet makes people gluttonous and lazy, but because it alters our biology in a way that changes our behavior.
Although the causes of obesity are complicated and diverse, resistance to leptin is the main reason why people gain weight and have difficulty losing it.
Leptin is the "master hormone" for the regulation of body fat.
Reference: https: //www.healthline.com/nutrition/leptin-101