The Skinny on Leptin
Leptin is an important hormone that plays a key role in regulating the amount of energy stored in adipose (fat) tissue. Leptin is secreted by the body's fat cells, and its secretion typically increases when the amount of adipose tissue increases. If your leptin signaling is working properly, increased energy intake signals your brain that there is plenty of energy available and that you can stop feeling hungry, stop eating and stop storing fat. In a healthy person, increased leptin levels also affect energy expenditure in a number of other ways, such as by causing an increase in the person's metabolic rate.
The Discovery of Leptin
Leptin was discovered in the mid 1990s when Jeffrey Friedman and his colleagues identified a gene in mice called obese (ob) that encodes a hormone that he later named leptin, after the Greek word leptos, which stands for thin. Mice that lack the ob gene, and thus do not produce leptin, eat constantly, are extremely obese, and develop type 2 diabetes due to insulin resistance. They are also infertile, suggesting that leptin is also important to reproductive health. However, when these obese mutant mice were injected with synthetic leptin, they started to lose weight and show signs of improved insulin sensitivity.
After this discovery, there was a lot of excitement because scientists hoped leptin supplements could hold the key to solving the obesity epidemic. Unfortunately, however, researchers soon discovered that many obese and overweight people actually have very high levels of leptin circulating in their blood. Furthermore, in clinical trials, administration of leptin did not prove to be an effective weight loss strategy in most obese people. The observations let to the development of a concept known as leptin resistance.
What is Leptin Resistance?
Leptin resistance is a lot like insulin resistance. If, over time, your body is exposed to too much leptin, you will become leptin resistant, just like your body can become resistant to insulin. In an individual with leptin resistance, leptin levels are high, but the hormone cannot reach its target site – the hypothalamus in the brain. This leaves the brain thinking leptin levels are too low and the body has not had enough food. In response, the brain begins to send signals to the body to increase food intake and store fat, leading to weight gain. Today, experts specialized in the topic, such as Byron J. Richards – a renowned leptin expert and the author of Mastering Leptin: Your Guide to Permanent Weight Loss and Optimum Health – believe that lifestyle and dietary changes aimed at improving leptin response in resistant individuals may be one of the most effective ways to combat obesity and related conditions.