Everyone – from people who are overweight or underweight to those with autoimmunity or chronic inflammation – is starting to talk about leptin. What exactly is leptin and how is it relevant to health? This post dives into the science of leptin.

What is Leptin?

Definition

Leptin is produced by the body’s fat cells. It has been called the “satiety hormone that causes weight loss.” It has also been called the “obesity hormone” or “fat hormone.” And lastly, it’s been nicknamed the “starvation hormone.”

Initial research hyped leptin’s alleged weight loss effects, but further studies revealed that leptin is not the weight loss pill everyone has been searching for. No proper clinical trials speak to its anti-obesity effects [1].

In fact, leptin levels increase exponentially, not linearly, with fat mass. This means that increased body weight can cause leptin to go much higher. Fat cells release more than 50 hormones and signaling molecules [2].

Function

Initially, leptin was known to be secreted by fat tissue, and circulate at levels directly proportional to the total amount of fat in the body [3].

However, it is now considered a multifunctional hormone that is produced by various tissues and organs including the placenta [4], kidney [5], salivary glands [6], and stomach [7].

Some people think that leptin is one of the big 4 hormones that determine weight. However, no proper research supports such a simplified approach, since many hormones and factors are involved in weight control.

Leptin is synthesized in fat tissue and receptors are found in higher concentrations in the hypothalamus and hippocampus [8].

Recent theories suggest that the more body fat we carry, the more leptin we produce. Some scientists say that leptin gets released into the blood and goes into the brain, where it sends a satiety signal to the hypothalamus. There, it tells 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. This is still a hypothesis, though [9, 10].

In some studies, chronically-elevated leptin levels have been associated with obesity, overeating, and inflammation-related diseases, including hypertension, metabolic syndrome, and heart disease [11]. However, no cause-and-effect has been established.

According to other theories, leptin resistance may contribute to hardening of the arteries. These theories are still somewhat controversial [11].

Normal Levels

Lab results are commonly shown