The hormone named leptin, being discovered 22 years ago, and named based on the Greek word leptos has been hailed as the key regulator of leanness. However, the key experiments that probe the function of this protein and unravel the precise mechanism of its action as a guardian against obesity.

Two decades ago, the scientists discovered the identity of a mouse obesity gene, finding that it encodes a previously unknown hormone made by the fat cells. This leads to a rare genetic deficiency, in which the people born with two defective copies of the gene are extremely obese, and their obesity is reversed by restoring their levels of leptin using daily injections.

Both in mice and people without the mutation, studies have shown that leptin plays and important role in regulating metabolism. Even though the researchers speculated that this protein plays a key role in helping healthy lean people remain thin. Paradoxically, obese mice and people how don’t have the defective obesity gene almost always have high levels of leptin.

The treatment with leptin has been approved in the United States since 2014, for the use in congenital leptin deficiency, as well as in an unusual syndrome of lipodystrophy, as the protein has not been readily available for clinical experiments.