Ghrelin and leptin are two appetite-controlling hormones that are produced by the body to tell the hypothalamus either to increase or decrease appetite. They act in opposite ways. Ghrelin is produced by the stomach lining and acts in a short-term manner to increase appetite in response to caloric intake at meals. Leptin is produced by fat cells, decreases the appetite over the long-term, and may possibly increase metabolism. Levels of ghrelin and leptin are affected by caloric intake, duration and quality of sleep, and body fat levels.
When researchers first discovered ghrelin and leptin, hopes were high that controlling these hormones could lead to breakthroughs in controlling weight loss. This has not been the case, because ghrelin and leptin interact with a host of other hormones and metabolic processes to affect appetite. Many complex environmental, genetic, and hormonal factors affect ghrelin and leptin levels and even can affect how well the body responds to levels of these hormones in the body.
Researchers have found that when they test a subject’s ghrelin and leptin levels before and after dieting, ghrelin levels increase after weight loss and leptin levels decrease. Both caloric restriction and fat loss appear to lower leptin levels while raising levels of ghrelin. This might be a factor in why diets tend to be unsuccessful, with at least 90 percent of dieters gaining back all the weight they lost. Frequently, they gain back even more weight than they lost.
When people gain weight, their ghrelin levels tend to be lower, while their leptin levels tend to be higher. Although it would seem to follow that someone who is obese and has high leptin levels would eat less in response, the opposite seems to be the case. Many researchers believe that many obese people have a form of leptin resistance, where the body has high levels of leptin, but leptin is not communicating with the brain effectively.
One study showed that a low-calorie, low-fat, high-carbohydrate diet increased leptin receptibility. These dieters still had lower levels of leptin in the body, but they appeared more receptive to its effects so that it took less leptin to feel satisfied. The results of a similar study suggested that high-fat diets increased leptin resistance, leading people to feel hungry even when their body had had enough food.
Sleep duration and quality can affect ghrelin and leptin levels. After a poor night’s sleep, ghrelin levels are elevated the next day, while leptin levels decline. Predictably, researchers have found that people who get less sleep on average tend to weigh more than people who get more sleep. This is also true for sufferers of sleep apnea, who tend to have poor-quality sleep. People with sleep apnea tend to have higher levels of obesity than people who do not have sleep apnea.