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Hormones That Control Appetite: Leptin and Ghrelin Facts

Linda Crampton is a writer and former teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

Leptin is a hormone that decreases our desire to eat. Ghrelin is a hormone that has the opposite effect and increases our appetite.

Leptin is a hormone that decreases our desire to eat. Ghrelin is a hormone that has the opposite effect and increases our appetite.

Important Hormones That Affect Appetite

Leptin and ghrelin are protein hormones that control our appetite. They are made in our bodies and were each discovered quite recently—leptin in 1994 and ghrelin in 1999. Leptin reduces our appetite and is produced mainly by the adipocytes (fat cells) in our white fat, which is also known as white adipose tissue. Ghrelin stimulates our appetite and is made chiefly by the stomach.

Researchers are still trying to discover exactly how the hormones work. Like other hormones, they have complex actions and multiple functions. The study of leptin and ghrelin is exciting, however, because in the future it may be possible to use these proteins—or our knowledge about how they work—to help control people's weight. We may be able to help leptin work more effectively or suppress the action of ghrelin, for example. The most important goal of the research is to reduce the increasing prevalence of obesity in many societies.

Leptin was discovered in 1994 and decreases our appetite.

Leptin was discovered in 1994 and decreases our appetite.

Discovery of Leptin

Leptin was discovered by Jeffrey Friedman from the Rockefeller University and Douglas Coleman from the Jackson Laboratory. They learned about the hormone and its effects by studying obese mice, but researchers soon found that the discoveries applied to humans as well.

The work of Friedman and Coleman was a major breakthrough in removing the impression that all obese people are overweight due to a lack of willpower in their eating habits. In fact, in the video below, Jeffrey Friedman says that he thinks that obesity is caused chiefly by biological problems.

Although leptin plays an important role in controlling body mass, it's not the only substance that has this function. Biological control of weight is a complex process that seems to involve many chemicals.

Jeffrey Friedman Discusses Leptin and Obesity

Production of the Hormone

A leptin molecule is made of 167 amino acids. Its name comes from the Greek word "leptos", which means "thin". The hormone is produced in the adipocytes of our white fat, or white adipose tissue (WAT). Each WAT adipocyte is a cell containing a large fat or triglyceride droplet.

Leptin is also made in much smaller quantities in other areas of the body, including in our deposits of brown fat or brown adipose tissue (BAT). BAT cells contain multiple small droplets of fat and a higher number of mitochondria than WAT cells. The mitochondria contain iron and give BAT cells a light brown colour.

The greater the amount of body fat, the higher the amount of leptin in the blood. In addition, women seem to make more leptin than men. The production of the hormone is controlled by the obese gene, which is also called the ob gene. Mutations (or changes) in this gene can create problems.

A leptin molecule (shown above) is a protein and consists of chains of amino acids.

A leptin molecule (shown above) is a protein and consists of chains of amino acids.

Leptin and the Hypothalamus

Excess food in our diet is converted into fat. As the amount of fat deposited in our adipose tissue increases, leptin is released from the adipocytes into the bloodstream. The larger the adipocytes become, the greater the amount of leptin released. The hormone travels to the brain via the bloodstream and attaches to the receptors on cells in the hypothalamus, the section of the brain that controls appetite. The binding process stimulates the hypothalamus to reduce our sensation of hunger. The fat deposition and the subsequent leptin release "tell" the hypothalamus that we've eaten enough food and no longer need to make eating a priority.

When the amount of fat stored in the body decreases, the amount of leptin released into the blood also decreases. When fewer leptin receptors are stimulated, the hypothalamus triggers our hunger and causes us to eat more food, which replaces our fat stores. Under normal conditions, leptin activity helps to keep our weight constant as the amount of body fat is adjusted.

Location of the hypothalamus in the brain

Location of the hypothalamus in the brain

Additional Actions of the Hormone

Though researchers know that leptin reduces hunger and that it affects the hypothalamus, the details of its actions are still being studied. The hormone seems to have multiple effects in the body and appears to influence the action of other chemicals.

Leptin receptors are present in additional parts of the body besides the hypothalamus. The hormone may affect the hypothalamus indirectly via its action on the receptors in these areas as well as directly by binding to receptors on the hypothalamus.

Different researchers have made different discoveries about the hormone's actions. The picture is not yet clear. Two items that are being investigated by multiple researchers in relation to leptin action are a signaling molecule known as Janus kinase 2 (or JAK2) and AgRP neurons in the brain. Researchers believe that the functions of JAk2 and leptin are connected. The neurons are known to be involved in the stimulation of eating behavior.

Hopefully, scientists will soon have a better understanding of the hormone's effects. Understanding all of leptin's actions could be very important for treating someone who has a problem linked to the chemical.

Read More From Owlcation

It’s important that we don’t fall into the trap of thinking “I’m overweight, therefore I must be deficient in leptin.” Body weight is controlled by multiple factors, and leptin’s actions are not completely understood. If someone tries to lose weight and is unsuccessful, they should consult a doctor.

The Problem With Leptin Supplements

Leptin supplements are available. Scientists say that ingesting these supplements isn't an effective way to lose weight, for several reasons. Since leptin is a protein, enzymes in the digestive tract break it down before it's absorbed into the bloodstream. In addition, the supplements generally don't contain any leptin, but instead contain substances that the manufacturers claim are leptin helpers, such as certain fatty acids.

Another problem is that researchers have discovered that most people don't lack leptin. In fact, obese people generally have a higher than normal level of the hormone, which seems logical since they have more adipocytes. Obese people may develop leptin resistance, however, a condition in which their body no longer responds to the presence of the hormone in their bloodstream.

Another cause of obesity is the complete lack of leptin. In this case, leptin provided by injections instead of in a supplement form does help people lose weight. The weight loss is often dramatic and very satisfying for the formerly obese person.

Sardines contain healthy omega-3 fat. People with leptin resistance should avoid unhealthy fats.

Sardines contain healthy omega-3 fat. People with leptin resistance should avoid unhealthy fats.

Leptin Resistance

Researchers still have many questions about why some some people appear to be leptin resistant while others are sensitive to the hormone. They do have some theories about the causes of the hormone resistance. The disorder may develop due to a malfunctioning of the leptin receptors in the hypothalamus, for example. If the receptors don't operate properly or have the wrong structure, leptin will be unable to bind to them and the hypothalamus won't reduce the desire to eat. Another possibility is that the leptin molecules may have an altered structure and be unable to attach to the receptors. Leptin resistance may also be due to the inability of the hormone to enter the brain.

Scientists need to determine the specific causes of leptin problems before they can devise treatments. It's a difficult task, but researchers are continuing to investigate the hormone and its actions. Until more effective treatments are created (and after a treatment is found), people diagnosed with resistance to leptin should exercise regularly, provided their doctor says that this is safe. Calorie restriction may not be possible, but it's still important to try to reduce sugar in the diet and to eat healthy fats instead of unhealthy ones. Some prescribed medications for other health problems may be helpful for patients. Obese people should visit their doctor regularly so that their health can be monitored and they can get advice that may improve their condition.

The interactions between substances and structures in the human body can be complex, but researchers are gradually discovering more information about the topic. The Medical Xpress links in the “References” section below shows some of the latest discoveries related to leptin and ghrelin.

The pituitary gland (colored red) in the brain produces a small amount of ghrelin.

The pituitary gland (colored red) in the brain produces a small amount of ghrelin.

Ghrelin Facts and Discovery

Ghrelin was discovered by Masayasu Kojima, Kenji Kangawa, and their colleagues. A ghrelin molecule is made of 28 amino acids. The gene that contains instructions for making ghrelin actually codes for a longer protein called preproghrelin. This protein is made of 117 amino acids and breaks down to make ghrelin and another protein. In 2005, researchers at Stanford University named this other protein obestatin and claimed—controversially—that it reduces appetite.

The stomach makes the largest quantity of ghrelin, but other parts of the body also produce it. The hormone and the receptor that it binds with in order to cause its effects have been found in several parts of the brain, including the hypothalamus, and in the pituitary gland, lungs, intestine, pancreas, kidneys, heart, and ovaries. Like all hormones, ghrelin is released into the bloodstream and travels to its target organ.

Obesity in Children and the Function of Ghrelin

Ghrelin is sometimes called the hunger hormone because it makes us hungry. It's also known as lenomorelin.

Some Effects of Ghrelin in the Body

A rise in the ghrelin level is linked to increased appetite. The hypothalamus contains ghrelin receptors as well as leptin ones. Researchers say that when the ghrelin molecules join to their receptors, the hypothalamus causes the sensation of hunger. Ghrelin also joins to receptors on the pituitary gland and triggers the production of growth hormone.

Ghrelin is secreted when the stomach is empty. When the stomach is stretched after eating, the production of the hormone decreases. The ghrelin level in our bloodstream is therefore highest just before we eat and falls shortly after we've eaten. A few hours after eating the hormone level rises again, stimulating us to eat our next meal.

Ghrelin produces a rapid effect once it's released. People injected with the hormone quickly become very hungry. Researchers have found that ghrelin also stimulates us to prefer high calorie foods compared to low calorie ones.

As the quotation below indicates, ghrelin is believed to have other functions. Some of the suspected influences of the hormone are not obviously related to food intake, though they may be indirectly so. These influences include learning, mood, memory, reward-seeking behaviour, the sleep-wake cycle, and even the aging process. Understanding the full details of the hormone’s actions may be difficult but should be very worthwhile as well as fascinating.

Ghrelin has been found to have a plethora of central and peripheral actions in distinct areas including learning and memory, gut motility and gastric acid secretion, sleep/wake rhythm, reward seeking behavior, taste sensation and glucose metabolism.

— T.D. Müller et al, via Molecular Metabolism

Ghrelin stimulates the desire for high calorie foods.

Ghrelin stimulates the desire for high calorie foods.

Sleep and Hormone Levels

Some researchers have shown that ghrelin and leptin levels are altered in people who lack sleep. The scientists have found that the ghrelin level is higher and the leptin level is lower in people who sleep for six hours or less a night compared to the levels in people who receive more sleep. They have also found that some of the people who sleep for an insufficient time gain weight.

The studies described above don't prove that lack of sleep is the reason for hormone level changes and weight gain, but the potential link is very interesting. Researchers already know that getting sufficient sleep is very important for our health. If it also helps to prevent weight gain, that's another bonus of getting an adequate amount of sleep each night.

Hope for the Future

Leptin research has led to a very successful treatment for obese people who make little or no leptin. Treating leptin resistance is a much harder job. There was great excitement when leptin was first discovered, but now people realize that more research is needed to make further use of the discovery.

Researchers are investigating the potentially beneficial effect of leptin in type 2 diabetes. This benefit seems to be independent of the hormone's ability to help some obese people lose weight. Obesity is a known risk factor for type 2 diabetes.

Like leptin, ghrelin is a very interesting hormone. Controlling its level in the body may someday be a helpful treatment for people who are having trouble losing excess weight and perhaps for helping other problems in the body.

Fully understanding the human endocrine or hormonal system is difficult for researchers, but the study could have many benefits. Hopefully, new therapies and medications will soon be developed for treating problems such as leptin resistance, obesity, and other problems influenced by leptin and ghrelin.

References

  • Information about leptin from WebMD
  • Leptin receptor deficiency (plus information about the hormone) from the US National Library of Medicine
  • The hormone's neural circuit from the EurekAlert news service
  • Leptin signaling from the US National Library of Medicine
  • Biology of leptin from the ScienceDaily news service
  • News about leptin from the Medical Xpress website
  • Ghrelin information from the Endocrine Society
  • Facts about the hormone from Colorado State University
  • An overview of ghrelin’s actions from the Molecular Metabolism journal
  • Stomach hormone ghrelin increases desire for high-calorie foods from the ScienceDaily news service
  • Sleep deprivation and hormone levels from Scientific American
  • News about ghrelin from Medical Xpress

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2012 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on August 07, 2014:

Hi, Peg. I certainly hope that scientists find a treatment for obesity. Thanks for the comment.

Peg Cole from North Dallas, Texas on August 07, 2014:

Quite interesting, AliciaC. Growing up, we were told that obesity was caused by hormones or a thyroid condition. Maybe the scientists are finally getting to the point of finding a remedy to replace all the fad diet pills on the market and the dangerous types of bariatric surgery.

Linda Crampton (author) from British Columbia, Canada on August 07, 2014:

I agree, ologsinquito. Avoiding gastric bypass surgery would be great! Thanks for the visit.

ologsinquito from USA on August 07, 2014:

It would be good to see more research in this area, so people don't have to do more risky and drastic things, such as bypass surgery, to treat obesity.

Linda Crampton (author) from British Columbia, Canada on June 10, 2014:

Thank you very much for the visit and the comment, Joe!

Joe from north miami FL on June 10, 2014:

Never heard of these particular hormones, they are very intriguing and I'm happy you have brought them to light here.

Linda Crampton (author) from British Columbia, Canada on November 07, 2012:

Thanks for the comment, crystolite. I appreciate your visit. It's a good idea for someone with appetite problems to visit a doctor to see if they have a hormonal problem, but buying supplements in a store - if they are available - probably won't be helpful.

Emma from Houston TX on November 07, 2012:

Thanks Alicia, this is a very good information for me because most times i lose appetite in the mornings. Am even going to get this for my grand parents. Thanks for sharing.

Linda Crampton (author) from British Columbia, Canada on November 06, 2012:

Thank you very much for the visit and the comment, Denise. I appreciate all the votes and the share, too!

Denise Handlon from North Carolina on November 06, 2012:

What a timely hub, Alicia. I've just now been reading more, researching, and attempting to understand these two hormones. It can be very confusing, but hubs, such as this one, are instrumental in clearing that confusion up. Thanks-will bookmark this one and share. Rated up/U/I/A

Linda Crampton (author) from British Columbia, Canada on October 31, 2012:

Thank you very much, drbj. I agree - Friedman and Coleman have made a very significant contribution to our knowledge of human biology. Hopefully their discoveries will lead to important medical treatments.

drbj and sherry from south Florida on October 31, 2012:

There is so little we really know about the human brain, Alicia, that it is stimulating to read such an intelligent and research-loaded hub as yours. Hormones are extremely complicated substances and we owe a debt to scientists like Friedman and Coleman who have learned so much about leptin and ghrelin. Thank you for sharing this awesome information. Voted Up, y'know.

Linda Crampton (author) from British Columbia, Canada on October 30, 2012:

Thank you for the comment, unknown spy!

Life Under Construction from Neverland on October 30, 2012:

Definitely a great gread! thanks for sharing!

Linda Crampton (author) from British Columbia, Canada on October 29, 2012:

Thanks, teaches. Yes, the apparent relationship between leptin resistance and Type 2 diabetes is very interesting. Perhaps leptin research will help our understanding of diabetes as well, as you say!

Dianna Mendez on October 29, 2012:

Fascinating topic and so interesting. I would imagine more research on this will prove helpful to those who suffer from diabetes as well. Great hub and voted up.

Linda Crampton (author) from British Columbia, Canada on October 29, 2012:

Hi, Peggy. I hope that the research is successful too. It would be great if researchers could safely correct biological problems that are causing weight gain! Thank you for the votes.

Peggy Woods from Houston, Texas on October 29, 2012:

This is very interesting Alicia. Hopefully more research will be continued and this will eventually be applied to humans whether they need to gain or lose weight for health reasons. An injection or series of injections would be easier on the body than more drastic weight loss surgeries...depending upon any side effects, of course. Surgery always has risks. Up votes!

Linda Crampton (author) from British Columbia, Canada on October 29, 2012:

Thank you for commenting, ignugent17. Leptin and ghrelin could be very useful to doctors in the future!

ignugent17 on October 29, 2012:

Wow great information. It is always great to read new things. I would be taking note of the protien hormones, Leptin, and Ghrelin.

Thank you for sharing. :-)

Linda Crampton (author) from British Columbia, Canada on October 28, 2012:

Thank you very much for the comment and the votes, Ingenira. Hormones aren't generally used as appetite suppressants, although an exception is the use of leptin injections for people who lack the hormone. Perhaps in the future hormones will be used to suppress appetites in people with other health problems, once researchers discover more about how the natural hormones in our bodies work!

Ingenira on October 28, 2012:

I like to have more of this leptin ! LOL.

Very interesting topic, I have heard of appetite suppressant, but not hormone that controls the appetite. Wondered if they are related.

Anyway, great hub ! Voted up, useful.

Linda Crampton (author) from British Columbia, Canada on October 28, 2012:

Thank you very much for the comment, Maren Morgan!

Maren Elizabeth Morgan from Pennsylvania on October 28, 2012:

Wow - fantastic information. Thanks!

Linda Crampton (author) from British Columbia, Canada on October 27, 2012:

Thank you, Bill. I appreciate your visit and comment!

Bill Holland from Olympia, WA on October 27, 2012:

Every once in awhile I will read a hub and come away feeling quite clueless. This was one of those hubs. I have never heard of either of these hormones......sigh!

Well, now I have, and it was quite interesting, so thank you for the education!

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