Leptin is a hormone that is produced by the body’s fat cells . It is often referred to as the “satiety hormone” or the “starvation hormone.”
Leptin’s primary target is in the brain, particularly an area called the hypothalamus. Leptin is supposed to tell the brain that we have enough fat stored, that we don’t need to eat, and that we can burn calories at a normal rate . It also has many other functions related to fertility, immunity, brain function and others .
However, leptin’s main role is long-term regulation of energy balance… the amount of calories we eat and expend, and how much fat we store on our bodies . The leptin system evolved to keep us from starving or overeating, both of which would have made us less likely to survive in the natural environment.
These days, leptin is very effective at keeping us from starving. But something is broken in the mechanism that is supposed to prevent us from overeating.
Leptin is Supposed to Tell The Brain That We Don’t 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 . Leptin is carried by the bloodstream and into the brain, where it sends a signal to the hypothalamus… the brain area that controls when and how much we eat .
The fat cells use leptin to “tell” the brain how much body fat they carry. Lots of leptin tells the brain that we have plenty of fat stored, while low levels of leptin tell the brain that fat stores are low and that we are at risk of starvation .
This schematic shows how leptin is supposed to work:
This kind 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.
Leptin Resistance May be The Main Biological Abnormality in Obesity
People who are obese 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 . Given the way leptin is supposed to work, these people shouldn’t be eating… their brain should know that they have plenty of energy stored.
However… the problem is that the leptin signal isn’t working. There’s a whole ton of leptin floating around, but the brain doesn’t “see” that it is there .
This condition is known as leptin resistance. It is now believed to be the main biological abnormality in human obesity. When the brain doesn’t receive the leptin signal, it erroneously thinks that the body is starving, even though it has more than enough energy stored.
This makes the brain change our physiology and behavior in order to regain the fat that the brain thinks we’re missing:
- Eating More: The brain thinks that we MUST eat so that we don’t starve to death.
- Reduced Energy Expenditure: The brain thinks we need to conserve energy, so it makes us feel lazier and makes us burn fewer calories at rest.