Leptin is a hormone released from fat tissue that signals the body's state of energy stores. It regulates energy intake, energy expenditure, appetite and metabolism. Leptin can be thought of as the "fullness hormone." It was believed that leptin was the key in controlling obesity because it regulated food intake and signaled fullness. However, studies have shown that leptin signaling is disrupted in obesity and results in uncontrolled food intake. Higher body fat percentage leads to greater leptin release, leading to less leptin sensitivity in the brain and less control over appetite and food intake.
Leptin's Function
Leptin is an adipose-derived hormone, meaning it is released from fat tissue and acts on receptors in the hypothalamus. The hypothalamus is the area of the brain responsible for autonomic functions, including hunger, heart rate, fat metabolism, body temperature and reproduction. Therefore, leptin is involved in regulating these functions, especially hunger and fat metabolism. When leptin is released, it binds to receptors in the brain and suppresses the actions of neuropeptide Y, a neurotransmitter that increases food intake and signals fat storage. So, leptin inhibits appetite, decreases food intake and controls fat metabolism by counteracting neuropeptide Y.
Leptin and Obesity
Leptin concentration and function in the body is directly proportional to body fat content. The more body fat a person has, the more leptin is released and circulating in the body. Logically, that would result in greater appetite control, less food intake and greater energy expenditure. Researchers thought leptin would be the key in controlling obesity, but study results revealed that the greater amount of leptin released, the less effective it is in the brain in controlling hunger and food intake. Leptin receptors in the brain become desensitized, suppressing leptin's normal effects on the body's autonomic functions. The result is uncontrolled feeding, leading to greater food intake and fat storage.
Leptin and Blood Sugar Regulation
Leptin is associated with the dangerous chronic conditions of obesity, especially diabetes. Leptin has been linked to the development of type 2 diabetes based on its involvement in regulating blood sugar levels. Leptin communicates with the liver in terms of handling its glucose stores. The liver stores glucose in the form of glycogen and releases it in order to maintain normal blood sugar levels in the absence of food. When leptin signaling is disrupted, usually due to obesity, blood sugar regulation is also disrupted.
Leptin and the Development of Diabetes
Studies showed that mice that ate too much and became obese but still produced leptin and had normal functioning receptors did not develop diabetes. On the other hand, genetically modified mice also ate too much and became obese, but because they did not produce leptin or have receptors, developed diabetes and died. The results of this 2005 study published in the journal "Cell Metabolism," illustrate that normal functioning leptin is involved in the signaling between the brain and the liver to regulate blood sugar levels, helping prevent diabetes and its complications.
Restoring Leptin Function
Because leptin is not the cure to obesity but plays a key role in the development of chronic diseases associated with obesity, itis important to find a way to control obesity and maintain or restore leptin function. Controlling obesity involves decreasing food intake and increasing energy expenditure. Following a low-calorie diet based on fruits and vegetables and lean protein, and limited in starches and simple sugars can result in weight loss and decreased body fat, which will increase leptin sensitivity and function. Also, a moderate exercise regimen that increases energy expenditure can also contribute to fat loss and leptin sensitivity while improving food intake control and fat metabolism.
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