Appetite-Regulating Hormones: Leptin

Our bodies have hormones that regulate every aspect of metabolism, and that includes appetite and weight regulation. Several hormones have been discovered that affect appetite and the development or prevention of obesity. There are four major such hormones: ghrelin, leptin, insulin, and peptide YY (PYY). This article focuses on leptin.

One bean on an otherwise empty white plate
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Simply stated, leptin is a hormone that suppresses appetite. It has been termed a “satiety factor” for this reason. Leptin is produced by adipose (fat) cells. The level of its production is thus in proportion to body fat. When body fat levels increase, so do levels of leptin, which then serves to suppress appetite and increase basal metabolic rate. When body fat levels fall, so do levels of leptin, and appetite suppression is removed, signaling to the body that it is time to eat again. Originally, this served the purpose of preventing starvation.

Leptin is sometimes thought of as ghrelin’s counterpart because ghrelin (another appetite-regulating hormone, produced by the stomach and duodenum) stimulates appetite as its levels rise. Because leptin can reduce food intake by suppressing appetite, it can induce weight loss; counter to that, because ghrelin can increase food intake by stimulating appetite, it can cause weight gain and obesity.

In 1994, the gene that produces leptin, known as the human obese (OB) gene, was discovered by Zhang and colleagues in mice. Leptin has been reported to have multiple biological functions, including immune and inflammatory responses, a role in the initiation of human puberty, a role in bone formation, and a role in wound healing, among others and in addition to its role in weight regulation.

What Affects Leptin Levels

Researchers have discovered a number of behaviors and factors that can either increase or reduce leptin levels in the body. The size and frequency of meals seem to play a role in the release of leptin from adipose tissue. In addition, the composition of a meal is important. In some studies, for instance, low-fat meals seemed to result in higher levels of circulating leptin than high-fat meals. There is also evidence that obese patients have become leptin-resistant, or resistant to the effects of leptin, and thus the normal biological regulatory pathway that tells the body when it is time to stop eating has been disrupted.

Too little sleep may also affect levels of leptin, resulting in lower levels and greater appetite (working in concert with ghrelin, as noted above). Getting the recommended seven to nine hours of uninterrupted sleep every night seems to help keep leptin levels where they should be in response to meals.

As might be imagined, due to its ability to induce weight loss, studies looking at different ways to utilize leptin and its functions for pharmacologic therapy have been ongoing for some time and are part of the continuing search for successful anti-obesity therapies.

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