what is leptin?

For patients struggling with obesity and weight, hormones often affect their overall health. Excess body fat can cause problems with weight and hormonal issues. Leptin is one of the hormones directly connected to body fat and obesity.

Leptin is sometimes called the satiety hormone. It helps inhibit hunger and regulate energy balance, so the body does not trigger hunger responses when it does not need energy. However, when levels of the hormone fall, which happens when an individual loses weight, the lower levels can trigger huge increases in appetite and food cravings. This, in turn, can make weight loss more difficult.

When the body is functioning properly, excess fat cells will produce leptin, which will trigger the hypothalamus to lower the appetite, allowing the body to dip into the fat stores to feed itself. Unfortunately, when someone is obese, that individual will have too much leptin in the blood. This can cause a lack of sensitivity to the hormone, a condition known as leptin resistance. Because the individual keeps eating, the fat cells produce more leptin to signal the feeling of satiety, leading to increased leptin levels.

Low levels of leptin are rare, but can occasionally occur. For a few patients, a condition known as congenital leptin deficiency keeps the body from producing leptin. Without leptin, the body thinks it has no body fat, and this signals intense, uncontrolled hunger and food intake. This often manifests in severe childhood obesity and delayed puberty. The treatment for leptin deficiency is leptin injections.

Many people believe that weight gain and loss is all about calories and willpower.

However, modern obesity research disagrees. Scientists increasingly say that a hormone called leptin is involved.

Leptin resistance, in which your body does not respond to this hormone, is now believed to be the leading driver of fat gain in humans

Leptin is a protein that’s made in the fat cells, circulates in the bloodstream, and goes to the brain. “Leptin is the way your fat cells tell your brain that your energy thermostat is set right,” Lustig says.

“Leptin tells your brain that you have enough energy stored in your fat cells to engage in normal, relatively expensive metabolic processes,” he says. “In other words, when leptin levels are at a certain threshold — for each person, it’s probably genetically set — when your leptin level is above that threshold, your brain senses that you have energy sufficiency, which means you can burn energy at a normal rate, eat food at a normal amount, engage in exercise at a normal rate, and you can engage in expensive processes, like puberty and pregnancy“.

Leptin is secreted mainly by white adipose tissue, and levels are positively correlated with the amount of body fat. Like many other hormones, leptin is secreted in a pulsatile fashion and has a significant diurnal variation with higher levels in the evening and early morning hours. Circulating leptin levels reflect primarily the amount of energy stored in fat and secondarily acute changes in caloric intake.

Because leptin is produced by fat cells, the amount of leptin released is directly related to the amount of body fat; so the more fat an individual has, the more leptin they will have circulating in their blood. Leptin levels increase if an individual increases their fat mass over a period of time and, similarly, leptin levels decrease if an individual decreases their fat mass over a period of time.

Obese people have unusually high levels of leptin. This is because in some obese people, the brain does not respond to leptin, so they keep eating despite adequate (or excessive) fat stores, a concept known as ‘leptin resistance’. This causes the fat cells to produce even more leptin. This is similar to the way people with type 2 diabetes have unusually high levels of insulin, as their body is resistant to the effects of insulin. The cause of leptin resistance is still unclear.

There is an extremely rare condition called congenital leptin deficiency, which is a genetic condition in which the body cannot produce leptin. In the UK, there are only about four families affected by this genetic condition.

Absence of leptin makes the body think it does not have any fat whatsoever and this results in uncontrolled food intake and severe childhood obesity. In addition, leptin deficiency may cause delayed puberty and poor function of the immune system. This condition can be well treated by leptin injections, which cause dramatic weight loss.