What is Leptin?

Leptin is essentially a hormone produced in fat cells, which circulates in the bloodstream and tells the brain has adequate fat reserves to use as energy. It is commonly referred to as the "starvation hormone". When we are dieting, our Leptin levels can fall and signal to the body that is "starving" - prompting us to eat more. 

When our Leptin levels are balanced, our appetite can also become balanced. A deficiency or outside of range results can also indicate one of the reasons for weight gain. 

How are Leptin levels controlled?

Your white adipose tissue (body fat) makes and releases leptin. White adipose tissue is the main type of fat in your body. It is located beneath your skin, around internal organs, and in the middle cavity of your bones. White adipose tissue serves as cushioning for various parts of your body.

The amount of leptin in your blood is directly proportional to the amount of adipose tissue your body has. The less body fat you have, the less leptin you have - the more body fat you have, the more leptin you will have.

Fat mass increases = Leptin level increases
Fat mass decreases = Leptin level decreases

What test measures leptin levels? 

A blood test can check the amount of leptin in a blood sample taken from a vein in your arm.

Healthcare providers don't routinely test for leptin levels, and the test isn't offered by all laboratories. Providers typically only consider ordering leptin tests if someone has obesity and has persistent hunger, or if a young child has class III obesity.  

What are normal leptin levels?

Normal value ranges for leptin levels may vary slightly among different laboratories. In general, normal ranges for leptin levels include:

  • Adults assigned female at birth: 0.5 - 15.2 nanograms per milliliter (ng/mL)
  • Adults assigned male at birth: 0.5 - 12.5 ng/mL

What happens when leptin levels are too high?

Since the amount of leptin in your blood is directly proportional to the amount of adipose tissue (body fat), having obesity results in high levels of leptin (hyperleptinemia). This can cause a lack of sensitivity to leptin, a condition known as leptin resistance. 

Other conditions associated with hyperleptinemia include:

  • Nonalcoholic fatty liver disease
  • Rabson-Mendenhall syndrome
  • Neurodegenerative disorders
  • Depression
  • Food addiction

What is leptin resistance?

If you have leptin resistance, your brain doesn't respond as it normally would to leptin. Since it is constantly stimulated by leptin, you don't get the sensation of feeling full or satiated. This causes you to eat more even though your body has enough fat stored. 

The seeming lack of leptin in leptin resistance also causes your body to enter starvation mode. In an effort to save energy your brain decreased your energy levels and makes you use fewer calories at rest. 

Leptin resistance further contributes to obesity and causes additional weight gain in the form of fat storage due to stimulating hunger and decreasing metabolism.