Ghrelin – The Hunger Hormone That Stimulates Appetite and Promotes Fat Storage In Your Body

Did you know that ghrelin, a hormone released by your stomach, can make you feel hungry?

It’s true!

The more ghrelin in your bloodstream the more likely you are to eat.

This is why it’s often recommended to drink water before meals or snack on something healthy before going out for dinner with friends.

Ghrelin also has other functions including regulating metabolism and growth hormones.

What Exactly is Ghrelin?

Ghrelin is produced in the gastrointestinal system, more precisely, in the gut. There are also other producing tissues, such as bone marrow cells.

Ghrelin is a 28-amino-acid peptide hormone that stimulates the release of growth hormone (GH) from the anterior pituitary gland.

It’s also present in the hypothalamus, placenta, duodenum, and adipose tissue. ^[1]

When Is Ghrelin Released?

Ghrelin levels typically peak before meals and decrease after eating has occurred (postprandial period). It means that ghrelin acts as a meal initiator.^[2]

It’s also produced in response to several different stimuli, including food deprivation and high-fat diets.

As the levels drop after eating, it promotes feelings of satiation and fullness, staying low for as much as three hours.^[3]

As a peptide hormone, its concentrations tend to vary depending on many factors such as age, sex, dietetic state, and metabolic condition.

Variations in specific cases

Pregnancy

Ghrelin concentration in the bloodstream rises to a peak at mid-pregnancy and then declines to its lowest by delivery.

Daily Blood Circulation

A study ^[4] showed how ghrelin concentrations varied over 24 hours for young female adults aged 18 to 24.

Ghrelin and Peptide YY (an appetite reducer) variables around mealtimes could be compared to finally show their generally inverse relation.

How Does Ghrelin Work?

Normally, when you start to get hungry, your stomach starts to growl, and your appetite increases. You may have a feeling of thirst or a headache because you’re dehydrated from not eating.

Otherwise, your brain starts to release serotonin, which makes you feel happy and satisfied when you eat something sweet.

Ghrelin, the hunger-stimulating hormone, is released in the body when it senses an empty stomach; helping to regulate hunger and appetite, it is released by cells in the stomach, and its levels rise when one feels hungry.

Note that ghrelin doesn’t last long in our system, so it needs to be released constantly. When ghrelin is released, it travels through our bloodstream to the brain.

With higher levels of the hormone, the appetite center of your hypothalamus becomes more active: certain receptors there, when activated, will release hunger-stimulating hormones such as neuropeptide Y and orexins.

These hormones will send signals to your stomach and small intestine to promote digestion and stimulate hunger feelings!

The Effects of Ghrelin on the Body

Metabolism

The whole ghrelin system has 4 receptors ^[5] (dAG, AG, GHS-R, and GOAT), responsible for a glucoregulatory action.

During that process, glucose will be released into the bloodstream to counteract low levels of energy to regulate the metabolism.

Ghrelin also affects other hormones ^[6] that are released during the digestive process. Levels of inhibiting hormones (of the secretin family), which are mainly responsible for secreting insulin, are all affected by ghrelin.

Those are gastric inhibitory peptide (GIP), glucagon-like peptide-I (GLP-I), and glucose-dependent insulinotropic peptide (also GIP).

The effects of ghrelin depend on where it is released and what type of cells or neurons it acts upon.

When secreted by tissues lining the stomach, for example, ghrelin causes appetite increase via NPY/AgRP activation ^[7] in hunger centers of the hypothalamus.

When secreted by X/A-like cells in the pancreas, ghrelin causes insulin secretion and blood glucose increase via stimulation of pancreatic islet β cells ^[8] by increasing islet particles (IP).

Sleep

Ghrelin also promotes sleep, especially during the day. Released by cells in the stomach lining, it acts to increase serotonin levels (which make you feel happy and satisfied when you eat something sweet).

It’s also stimulated by fasting or food deprivation, so it can help induce sleepiness after a long day of not eating.

Sleep deprivation, however, alters ghrelin levels and may disrupt how it affects sleep. Those who deprive themselves of sleep for extended periods may also deplete their levels of the hormone and suffer from insomnia.

So, to maintain a healthy lifestyle, it’s recommended to avoid sleep deprivation and give your body the time it needs to rest.

Emotional State

Ghrelin can also help keep your mood stable if you have been diagnosed with depression or anxiety because it reduces stress-related cortisol production.

Hence, it leads to better mental health outcomes for those who suffer from these disorders.

Reproductive system

Ghrelin also affects reproduction: it stimulates gonadotropin release from the anterior pituitary gland; specifically GH release, which induces growth of the gonads (glands for developing sex cells) and gametogenesis (the process).

Nevertheless, experiment results have shown that ghrelin inhibited the secretion of the luteinizing hormone (LH) while leaving the follicle-stimulating hormone (FSH) intact.

Ghrelin is produced in the fetal lungs at a very early stage and aids lung development. It also stimulates the production of surfactant proteins that maintain normal alveolar stability and lung fluid balance.

Levels of ghrelin in the umbilical cord blood are associated with baby weight. High levels at birth may be a cause for “oversized babies”; low levels could mean an underweight baby.

Types of Symptoms caused by the Lack of Ghrelin

The following are some of the various symptoms that may be caused by a lack of ghrelin in the body:

• Increased appetite
• Extreme hunger
• Lack of hunger
• Stomach growling
• Nausea
• Headache
• Irritability
• Depression
• Insomnia

Associated Diseases & Disorders

As you can see, ghrelin is a hormone that has many functions in the body and it’s crucial for many of our daily functions.

However, the hormone has been found to have abnormally too high or too low levels in blood plasma and these can vary between different periods, depending on their weight or any related disease.

Not to mention the many interactions between ghrelin and other important hormones in the body, which are responsible in specific quantities for various functions, body behaviors, and typical effects.

PCOS (Polycystic Ovary Syndrome)

For many people with PCOS, ghrelin may be their best friend when it comes to weight loss because they do not produce enough leptin or insulin, both hormones that help control appetite.

Apart from appetite and sleep modulation, ghrelin may also play a part in fertility in women with PCOS.

Given that ghrelin levels in women with PCOS are elevated after weight loss, ghrelin can cause obesity and an exacerbation of reproductive and metabolic complications in such patients.

Women need to be monitored for this potential over-activation of ghrelin by intraperitoneal (inside the transparent membrane around the abdominal cavity) or intravenous administration of leptin antagonist regularly to maintain optimal weight control.

Researchers now believe that this hormone might be used as a treatment for weight loss in PCOS cases.

Lymphedema

The condition is typically due to an accumulation of lymph fluid within tissues or limbs due to impaired drainage.

The impairment may be a symptom of trauma (e.g., surgery), chronic infection, hereditary abnormality of the lymphatic system, or other factors.

This condition is often associated with obesity and lack of exercise because these two things can worsen the symptoms. So ghrelin could potentially be used in treatment to help patients lose weight and improve their mobility.

Anorexia

For maintaining a healthy weight, ghrelin levels should be high. Individuals with anorexia nervosa have periods of growth hormone release and ghrelin decreases during starvation.

Low levels of ghrelin can lead to anorexia nervosa. This is usually possible since it then becomes easier to feel full on fewer calories with those low levels.

Anorexia nervosa is an eating disorder that causes people to have self-destructive urges associated with food.

People who suffer from this condition often have low levels of ghrelin, which can lead to malnutrition and eventually death.

The situation is the opposite of what we see in healthy people. Ghrelin levels are high, meaning that they desire food frequently.

Ghrelin also affects another hormone, the leptin hormone. This hormone tells you when to stop eating.

Ghrelin will eventually reduce the leptin levels, which occurs in anorexia nervosa patients in the attempt of starvation.

In studies involving mice (post non-caloric diets), significant ghrelin brought about satiating behaviors in mice. Later, ghrelin proved to be a strong deterrent of hypoglycemia and even death.

Weight Management

Ghrelin supplementation has certain benefits, like promoting weight loss and fat loss. Ghrelin levels increase shortly before each meal, stay high while you’re eating, and decrease soon afterward.

This is what causes the feeling of fullness that we feel after eating. This means that ghrelin encourages weight loss because it makes us feel satiated faster than other hormones.

In addition to being a hunger-stimulating hormone, ghrelin also stimulates fat storage (lipogenesis), telling the body to store more energy after eating (postprandial).

This can be beneficial for weight loss programs since ghrelin directly creates cravings for higher-calorie foods; even through an increased appetite.

So if ghrelin levels are too high they can eventually lead to overeating, and thus, weight gain if prolonged over time.

Ghrelin also provides an indispensable source of energy for muscles. When you are fasting or on a low-calorie diet, ghrelin levels decrease which can cause muscle wasting (atrophy).

Leptin is another hormone that affects hunger and weight loss. The hormone is responsible for the sensation of feeling full as well as the conversion of fat to energy.

When levels of ghrelin are too high, it means that leptin levels are low. This can lead to obesity, which is the opposite of what happens when ghrelin levels are too low.

It is especially in the case of Prader–Willi syndrome-induced obesity (PWS), with that ghrelin-leptin ratio, where people eat more than they should be eating.

The opposite happens when an individual is underweight where their ghrelin levels are low.

The essential thing here is to learn to keep these hormones in the right balance for your metabolism to function correctly. And there exist many ways out there!

Read more: 5 Ways to Control Your Hunger Hormone with Functional Medicine

Cancer-induced Cachexia

Cachexia is a symptom of many different diseases, but it’s been well-established that cancer patients are the most likely to experience it.

Its characteristics consist of weight loss, weakness, and lack of appetite, which lead to malnutrition and an impaired immune system.

Ghrelin levels have been correlated with this condition because cancer cells produce ghrelin, which can cause serious consequences for the body if left untreated.

One way to treat this issue is through surgery or radiation therapy because these therapies can generally slow down or stop tumor growth.

In addition, these treatments may also reduce the production of ghrelin in tumor cells which may relieve symptoms associated with cachexia!

Gastric Bypass Surgery

First of all, how important would ghrelin be to the body? To demonstrate this, we’ll consider a total gastrectomy (surgically removing all the stomach, where lies most of the hormone).

After such an operation, the decrease in ghrelin can get compensated through production by the intestines and pancreas.

But for a better increase of ghrelin, we would mostly count on two adrenal regulators, glucose and norepinephrine.

Conclusion

The next time you feel like snacking on something unhealthy because you’re feeling a little stressed or anxious, try drinking some water first.

Remember that ghrelin levels will go down as time passes, and soon you should be able to think more clearly without the urge to eat something unhealthy!

Andreea Doireann

Researcher and Writer

Andreea is a fitness enthusiast with a keen interest in nutrition. She has gone from 98Kg to 70Kg through relentless hard work and getting her nutrition right with the help of a personal trainer.

She writes articles to empower anyone to take control and not let go of their mental and physical health.

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