What Is Ghrelin?

Medically Reviewed by Shruthi N, MD on August 30, 2024
11 min read

Ghrelin is a hormone your stomach makes that signals your body when you're hungry. You might think of it as an "on switch" for appetite.

Your small intestine, pancreas, and brain also release small amounts of ghrelin. Another name for ghrelin is the "hunger hormone." 

Ghrelin vs. leptin

Ghrelin and leptin are both hormones that regulate how much you eat, but they do it in opposite ways. Ghrelin increases appetite. Leptin decreases it. 

Leptin helps regulate your body's energy balance. Your fat cells release leptin when you've stored enough energy, to tell your body that you've had enough to eat. By reducing appetite, leptin can help with weight loss. Leptin actually comes from the Greek word meaning "thin."

Ghrelin's main job is to stimulate appetite. This hormone also:

  • Regulates metabolism, which is how your body uses and stores energy
  • Controls how your body releases insulin and glucagon, hormones that control blood sugar levels
  • Directs your pituitary gland to release growth hormone
  • Protects your muscles, bones, and heart

Ghrelin and appetite

Ghrelin earned the nickname "hunger hormone" because of its effects on appetite. This hormone acts on the hypothalamus, the part of your brain that makes hormones that control appetite. Ghrelin also boosts appetite through its effects on the amygdala, your brain's reward center. These actions cause you to feel hungry and make you want to eat more.

Ghrelin and stress

Normally, ghrelin levels in your blood rise when you haven't eaten in a while and drop when you're full. But research has shown that ghrelin levels also rise in response to stress. That may be why people eat when they're upset, also known as "stress eating." Some researchers think ghrelin might help protect against the harmful effects of stress on the body, but it can also contribute to weight gain and obesity.

What stimulates ghrelin release?

Hunger triggers ghrelin release. When your stomach is empty, levels of this hormone in your blood rise. Ghrelin levels are highest right before a meal. Levels should drop back down after you eat. 

Different nutrients affect ghrelin levels in different ways. Carbohydrates and proteins slow ghrelin release, and fats increase it. 

Because ghrelin stimulates hunger, it can work against weight loss. The level of ghrelin in your blood goes up when you eat less to lose weight. It's your body's defense mechanism to prevent you from getting too thin. A higher ghrelin level is why you might feel hungrier when you diet, and why it can be so hard to lose weight. 

Ghrelin and gastric bypass

Gastric bypass is a type of weight loss (bariatric) surgery. The surgeon makes a small pouch out of the stomach and then attaches it to the small intestine. This smaller pouch leaves less room for food.

Researchers have found that ghrelin levels drop for a few months after gastric bypass surgery. Because the stomach makes ghrelin, when it shrinks, it produces less of this hormone. Lower ghrelin levels may help people feel less hungry and lose weight after bariatric surgery. After a few months, ghrelin rises to levels similar to those in people who are at a healthy weight. But the increase in ghrelin doesn't seem to make people regain weight after gastric bypass.

Ghrelin and weight gain

This hormone could contribute to weight gain in a few ways. Ghrelin acts on your brain to stimulate appetite and make you feel hungry. It also slows down your body's metabolism so that you burn less fat. And it increases the amount of fat your body stores, especially in your belly. 

Ghrelin and obesity

Obesity means that you have a body mass index (BMI) of 30 or higher. Some studies have shown that people who have obesity have lower ghrelin levels than those who are at a healthy weight. 

People with obesity may be more sensitive to ghrelin. That means it takes less of this hormone to make them feel hungry and they may eat more as a result. We need more research to fully explain the link between ghrelin and obesity.

Your body releases more ghrelin after you haven't eaten for a while. Ghrelin levels can increase if you eat much less food; for example, if you're on a strict diet. That ghrelin spike is the result of your body trying to hold onto more calories and fat. You'll feel hungrier as ghrelin signals your brain to eat. High ghrelin levels are also linked to inflammation and several medical conditions.

Ghrelin and sleep

Usually while you sleep, leptin levels rise and ghrelin levels fall. When you don't get enough sleep, these hormones reverse: Leptin levels fall and ghrelin levels rise. The increase in ghrelin makes you feel hungrier. It also increases your cravings for high-carb, high-fat foods. That's why people who are sleep-deprived tend to gain weight.

Ghrelin and anorexia

Anorexia nervosa is an eating disorder where people restrict food, exercise too much, make themselves throw up, or misuse laxatives to lose weight. The condition can be life-threatening.

Researchers have noted higher ghrelin levels in people with anorexia, compared to those without this eating disorder. Normally, ghrelin levels drop after a meal. But in people with anorexia, ghrelin levels stay high after eating, possibly to encourage them to eat more food. After people with anorexia have successful treatment and gain weight, their ghrelin levels drop. Researchers are studying whether a drug that blocks ghrelin might someday help people with anorexia regain weight.

Cachexia

Severe weight loss and muscle loss, which doctors call cachexia, is a common problem in people with late-stage cancer. Having cachexia can make people less responsive to treatment, increase cancer complications, and reduce survival. Because ghrelin increases appetite and fat storage, researchers have been studying this hormone as a possible treatment for cancer-related cachexia.

The research on ghrelin for cancer-related cachexia is promising but still in its very early stages. Experts say we need better-quality studies to learn whether boosting ghrelin levels is safe, and if it can improve weight gain and increase muscle mass.

Celiac disease

This condition involves an immune reaction to gluten, a protein in wheat, barley, and rye. If you have celiac disease, when you eat foods that contain gluten, your immune system attacks the gluten in your small intestine. That attack causes symptoms like diarrhea, fatigue, and weight loss.

People with celiac disease may have higher-than-normal ghrelin levels as their body tries to prevent weight loss. Ghrelin levels usually drop once they start on a gluten-free diet.

Inflammatory bowel disease (IBD)

IBD includes Crohn's disease and ulcerative colitis. Both conditions cause inflammation in the digestive tract, with symptoms like diarrhea, belly pain, and weight loss.

People with active IBD have higher ghrelin levels, which could be due to weight loss. Researchers have looked at ghrelin as a possible treatment for IBD, because it lowers inflammation, increases appetite, and helps digested food move more easily through the intestines. It's still too early to know whether ghrelin will work as an IBD treatment.

Prader-Willi syndrome

A very high ghrelin level is also a sign of Prader-Willi syndrome. People with this rare, inherited condition constantly feel the urge to eat and never seem to fill up. They may become very overweight as a result. Their ghrelin levels stay high, even after they eat. A delayed feeling of fullness may at least partly explain why people with Prader-Willi syndrome are so hungry all the time. 

Growth hormone deficiency

Ghrelin helps to control the pituitary gland's release of growth hormone. This hormone helps children grow and regulates metabolism and blood sugar levels in adults.

In growth hormone deficiency (GHD), the pituitary gland doesn't release enough growth hormone to meet the body's needs. As a result, children with GHD are shorter than usual. Adults with this condition have problems with metabolism. People with GHD may have higher ghrelin levels as their body tries to compensate and increase growth hormone production.

Ghrelin levels naturally drop after a meal when your stomach is full. People with obesity have lower ghrelin levels, and their bodies may be more sensitive to this hormone. Low ghrelin is also linked to a few diseases.

Chronic gastritis and H. pylori infection

Gastritis is inflammation in the stomach lining. Helicobacter pylori (H. pylori) bacteria cause gastritis by inflaming and irritating the stomach. Because the stomach produces ghrelin, damage to this organ can disrupt ghrelin production. People with chronic gastritis and H. pylori infection may have lower ghrelin levels, but levels should increase after the H. pylori infection is treated.

Functional dyspepsia

Bloating, belching, belly pain, and nausea after you eat are symptoms of functional dyspepsia. This collection of digestive symptoms doesn't have any obvious cause.

Ghrelin levels are low in some people with functional dyspepsia. Because ghrelin helps your stomach empty faster, experts think this hormone might play a role in functional dyspepsia by slowing stomach emptying, which could lead to bloating and other symptoms. Researchers are looking into ghrelin as a possible treatment for functional dyspepsia.

Irritable bowel syndrome (IBS)

IBS is a common gut condition that causes symptoms like diarrhea, constipation, belly pain, bloating, and gas. People with IBS have low levels of ghrelin, both before and after they eat, compared to people without this condition. Ghrelin may contribute to IBS symptoms by slowing the movement of food through the digestive system.

Hyperthyroidism

Thyroid hormones control how your body uses energy, called metabolism. In hyperthyroidism, the thyroid releases too much of its hormones.

Some studies have found lower ghrelin levels in people with hyperthyroidism. One possible reason is that the extra thyroid hormone causes your body to make more insulin – a hormone that controls blood sugar levels. Insulin may block the release of ghrelin. In studies, ghrelin levels increased when people received treatment for hyperthyroidism.

Ghrelin levels naturally rise when you're hungry and fall after you eat. But if your ghrelin levels are higher than normal and are making you gain weight, there are a few possible ways to lower them.

Ghrelin blockers

Researchers are studying a few substances that block ghrelin. One is liver-expressed antimicrobial peptide 2 (LEAP-2), a protein made in the liver. LEAP-2 blocks the effects of ghrelin on appetite, blood sugar levels, and growth hormone release. L-cysteine, an amino acid, may reduce ghrelin production in the stomach and suppress hunger.

Blocking ghrelin might one day be a treatment for obesity. The research on ghrelin blockers is promising, but it's still in the early stages.

Ghrelin supplements

A few supplements have been studied to lower ghrelin levels, reduce appetite, and promote weight loss:

  • L-cysteine. This amino acid might help to lower ghrelin levels and decrease appetite.
  • Green tea extract. In one study, women with excess belly fat who took a high-dose green tea extract for 3 months had lower ghrelin levels and lost weight.
  • Fatty acids. Rats that ate fish oil and olive oil in studies had lower ghrelin levels.
  • Piper betel leaf extract and Dolichos biflorus. People who took an herbal supplement containing these plant extracts for 8 weeks had lower ghrelin levels and lost weight.

Supplements aren't FDA-evaluated or regulated. There isn't enough published research to confirm whether they lower ghrelin or promote weight loss. Some supplements might have side effects or interact with medicines you take. Talk to your doctor before trying any supplement to make sure that it's safe for you.

Eat a balanced diet

Certain foods affect ghrelin levels more than others. For example, high-protein foods (fish, beans, and skinless chicken) and healthy carbohydrates (oats, vegetables, and quinoa) lower ghrelin levels. Foods that are high in fat are less likely to lower ghrelin levels.

A balanced diet may help regulate ghrelin levels. In one study, when people who had obesity ate a version of the Mediterranean diet rich in vegetables, poultry, fish, and walnuts, and cut out processed foods and red meats, their fasting ghrelin levels went up and they lost more fat around their belly. Researchers think that the higher levels of ghrelin have a link to better health of the heart, blood vessels, and metabolic system. 

Get enough sleep

Levels of leptin, an appetite-suppressing hormone, naturally rise while you sleep, while ghrelin levels drop. Research finds that people who regularly don't get enough sleep have lower leptin and higher ghrelin levels at night. They also have a bigger appetite, more cravings for high-calorie and high-carb foods, and a higher body mass index (BMI). 

Keep an exercise routine

You have many reasons to exercise, including weight management and improved blood sugar levels. Some studies show that working out also temporarily lowers ghrelin levels. Why this happens isn't clear. The drop in ghrelin may be more due to weight loss than to exercise. 

Manage your stress

One reason why you might stress-eat is because ghrelin levels rise when you're under stress. People who have obesity have higher ghrelin levels, and their levels stay high longer in response to stress than people who are at a healthy weight.

Some researchers think ghrelin might act like an antidepressant and buffer some of the harmful effects of stress on our bodies, even though the ghrelin boost is usually short-lived. You can help keep stress under control with techniques like deep breathing, meditation, and exercise. 

Maintain weight

When you gain a lot of weight, your body may become more sensitive to the effects of ghrelin. It takes less ghrelin to make you feel hungry, so you eat more. Going on a restrictive diet makes ghrelin levels rise as your body tries to hold onto more calories. Keeping your weight steady and avoiding yo-yo diets will help prevent swings in ghrelin levels.

Ghrelin is a hormone your stomach and other organs produce. It has several functions in the body, including controlling the release of hormones that control growth and blood sugar levels. It signals your brain that you're hungry. A lack of sleep, high stress levels, and an unhealthy diet are just a few of the things that can boost ghrelin levels, make you feel hungrier, and promote weight gain.

What triggers ghrelin release?

Ghrelin levels naturally rise in between meals. Your stomach releases this hormone when it's empty, to send a signal to your brain that it's time to eat.

How can I reduce ghrelin?

You can lower ghrelin levels by eating a balanced diet, getting enough sleep each night, exercising regularly, and controlling stress.

What happens when ghrelin levels are high?

When ghrelin levels are high, you feel hungrier so you may eat more. Consistently high ghrelin levels could lead to weight gain.

What turns off ghrelin?

After you eat and your stomach is full, ghrelin production stops.

What foods activate ghrelin?

High-fat foods like red meat or cake may activate ghrelin.

What suppresses ghrelin secretion?

Eating more protein and healthy carbs like whole grains, exercising, getting enough sleep, and reducing stress may prevent ghrelin spikes.