Leptin, the Body Fat Hormone

Photograph of Assorted Nuts Courtesy of Stephen Orsillo
Photograph of Citrus and Parsley Courtesy of Sandra Cunningham
Photograph of Man Exercising Courtesy of Suhendra Utet
Photograph of Measuring Tape Courtesy of Irma Marren

Leptin is a protein secreted by adipose (fat) tissue. It was named after the Greek word leptos, meaning “thin.” The more stored fat a person has, the more leptin is secreted. Of course we used to think that fat just sort of, well, grew around the midline and thighs, and was inert. Now scientists know that fat is actually an active organ and makes hormones such as leptin.

Leptin binds specific receptors in the body tissues and organs. High leptin levels also signal the brain to decrease appetite and food intake. Leptin also interacts with the areas of the brain that involves motivation to eat and reward for eating as well as the feeling of being full.

Overeating, high sugar levels, high insulin levels, internal steroids and estrogens all increase leptin levels in the bloodstream.

Losing weight, a lack of body fat such as in patients with anorexia, HIV related weight loss, fasting state, adrenaline, thyroid hormones, testosterone all decrease leptin levels in the body.

Many of us think we have a hormonal reason for being overweight. The truth is that leptin deficiency is exceedingly rare. Rare cases of leptin deficiency are seen in childhood when children eat tremendous amounts of food and become morbidly obese. Because of their leptin deficiency, these children do not enter puberty. It is essential in obese children to determine if leptin deficiency is playing a role. These children respond to pharmaceutical replacement with leptin.

So how about the rest of us? Can leptin injections help with weight loss? Well, the truth is, most people who are obese already have very high levels of circulating leptin. They should lose weight due to the effects of leptin on the appetite and satiety centers in the brain but they don’t! Unfortunately, most people’s brains become resistant to the effects of chronically elevated leptin levels, just like diabetics become resistant to the effects of high insulin in their bloodstream. The exact mechanisms for this leptin resistance is unknown.

So it turns out that leptin is not the magic weight loss drug we thought it could be. Early studies with high dose leptin admininstration did not lead to significant weight loss. Some researchers propose that the addition of a pancreatic hormone called amylin may sensitize the body’s response to leptin. Preliminary studies suggest that the addition of an analogue of amylin called pramlintide may help aid weight loss, although like most weight loss studies, the patient withdrawal rate in this study was high, making conclusions difficult to interpret.

Where leptin may play a role is in the maintenance of weight loss. It is hypothesized that decreasing leptin levels in people who have lost weight increases their appetite and reverses the weight loss they attained. Hence the yo-yo weight loss/weight gain cycle that is so familiar to many of us. So in the future, it may be possible to maintain that hard earned weight loss with the use of exogenous leptin. For right now though, eating healthy portions and exercising are the best way to maintain that weight loss!

Last updated by Dr. Vee on February 27, 2011

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