Leptin is a hormone that is manufactured in the adipose tissue of the human body; it is comprised of 167 amino acids. Leptin was discovered in 1994 by geneticist Jeffrey Friedman. It was considered a groundbreaking discovery in terms of appetite regulation. Friedman and his team named this hormone they found leptin, which in Greek means leptos, or thin. The amount of leptin circulating in the body is proportional to the amount of fat an individual has. The dominant role of leptin is to signal energy deficiency in the brain. The process of eating combines behaviors that are both psychological and physiological in nature. There has been an increasing interest in the role that leptin plays in obesity.
Leptin and the Brain
Leptin is regulated by a gene called the ob gene. There are leptin receptors throughout the body, but this hormone is most active in the brain. After a meal, the fat cells in your body signal the release of this hormone and it travels to the hypothalamus, which is the area of the brain that regulates the appetite; the leptin bonds with receptors located there. The process for appetite regulation continues as the leptin receptors, which control the release of neuropeptides, is stimulated. Neuropeptides are small proteins that signal the appetite to turn on or off.
Neuropeptide Y
Neuropeptide Y is the peptide that turns the appetite on and the metabolic rate down. Once leptin has bonded with its receptors in the brain, it shuts off neuropeptide Y and begins sending messages to the body to start burning calories. When the body is functioning optimally, leptin even has the capability to tap into the body's deep, visceral fat stores and help reduce them, which reduces your chances of serious obesity-related diseases such as coronary heart disease and diabetes. Your body also experiences a surge of leptin while you are sleeping, which helps keep your metabolism elevated during your body's longest period of rest and also stimulates the thyroid to release thyroxine, another important metabolic hormone.
Leptin and Obesity
Leptin levels in the body can vary for many different reasons. While it would seem that low leptin levels would be the primary cause of obesity, researchers are finding extremely high levels of leptin in those that are clinically obese. According to Jillian Michaels in her book, "Master Your Metabolism", the more fat that you carry around, the more leptin you produce and the body processes a reaction similar to what is experienced with insulin resistance. When the body constantly sends out excess levels of leptin in response to overeating, the receptors located in the body become worn down and stop recognizing the hormone. When this happens, neuropeptide Y never gets shut off, hunger remains, but the metabolism slows down drastically.
Factors That Interfere with Leptin
While obesity is one of the primary causes of leptin resistance in the body, other factors that can affect leptin levels include high-carbohydrate diets that are not complex in nature, high trans-fat diets, infections, not enough REM sleep or less than 7 to 8 hours of continuous sleep, and certain infections. Signs that might be indicative of too much leptin include feelings of constant hunger, high blood pressure, high cholesterol, increased inflammation and diabetes.
References
- The University of Edinburgh: Obesity
- "Master Your Metabolism": Jillian Michaels;2009
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