Weight loss can be tough, but maintaining your weight after a diet is even harder.

Research shows a large percentage of dieters regain all the weight they lost within just one year (1). Weight re-gain is partially due to your body’s appetite and weight-regulating hormones, which try to maintain and even re-gain fat (2, 3, 4, 5).

Ghrelin, the “hunger hormone,” plays a key role because it signals your brain to eat (6, 7, 8).

Its levels increase during a diet and intensify hunger, making it hard to lose weight (9, 10).

Here’s everything you need to know about this hormone and how to keep it in check.

What is Ghrelin?

Ghrelin is a hormone produced in the gut. It is often termed the hunger hormone, and sometimes called lenomorelin.

It travels through your bloodstream and to your brain, where it tells your brain to become hungry and seek out food.

Ghrelin’s main function is to increase appetite. It makes you consume more food, take in more calories and store fat (7, 11).

The graph below shows how rats injected with the hormone had a rapid increase in weight (12).

In addition, it affects your sleep/wake cycle, reward-seeking behavior, taste sensation and carbohydrate metabolism (7, 11).

This hormone is produced in your stomach and secreted when your stomach is empty. It enters the bloodstream and affects a part of the brain known as the hypothalamus, which governs your hormones and appetite (11, 13).

The higher your levels, the hungrier your get. The lower your levels, the more full you feel and the easier it is to eat fewer calories.

So if you want to lose weight, lowering your ghrelin levels can be beneficial.

Ghrelin may sound like a terrible, diet-wrecking hormone. However, in the past it played a role in survival by helping people maintain a healthy level of body fat.

These days, if you under-eat or struggle to gain weight, higher ghrelin levels may help you consume more food and calories per day.

Bottom Line:

Ghrelin is a hormone that sends a signal to your brain to feel hungry. It plays a key role in regulating calorie intake and body fat levels.

What Causes Ghrelin to Rise?

Ghrelin levels typically rise before a meal, when your stomach is empty. Then they decrease shortly after, when your stomach is full (14).

While you might assume obese people have higher levels, they may just be more sensitive to its effects. In fact, some research shows their levels are actually lower than in lean people (15, 16, 17).

Other research suggests that obese people may have an overly active ghrelin receptor, known as GHS-R, which leads to increased calorie intake (6, 7).

Yet regardless of how much body fat you have, ghrelin levels increase and make you hungry when you start a diet. This is a natural response by your body, which tries to protect you from starvation.

During a diet, your appetite increases and your levels of the “fullness hormone” leptin go down. Your metabolic rate also tends to decrease significantly, especially when you restrict calories for long periods of time (18, 19).

For obvious reasons, these adaptations can make it significantly harder to lose weight and keep it off.

Your hormones and metabolism adjust to try to re-gain all the weight you lost.

Bottom Line:

Ghrelin levels can rise during a diet, increasing hunger and making it harder to lose weight.

How Your Levels Change During a Diet

Within a day of beginning a diet, your ghrelin levels will start to go up. This change continues over the course of weeks.

One study in humans found a 24% increase in ghrelin levels on a 6-month diet (20).

In another 3-month weight loss diet study, researchers found the levels nearly doubled from 770 to 1,322 pmol/liter (21).

During a 6-month bodybuilding diet, which attains an extremely low level of body fat through severe dietary restrictions, ghrelin increased by 40% (22).

These trends suggest that the longer you diet — and the more body fat and muscle mass you lose — the higher your levels will rise.

This makes you hungrier, so it becomes much harder to maintain your new weight.

Bottom Line:

Ghrelin levels increase significantly on a weight loss diet. The longer the diet, the more your levels will increase.

How to Lower Ghrelin and Reduce Hunger

Ghrelin seems to be a hormone that can’t be directly controlled with drugs, diets or supplements.

However, there are a few things you can do to help maintain healthy levels:

  • Avoid weight extremes: Both obesity and anorexia alter ghrelin levels (23, 24)
  • Prioritize sleep: Poor sleep increases your levels, and has been linked to increased hunger and weight gain (25, 26).
  • Increase muscle mass: Higher amounts of fat-free mass or muscle are associated with lower levels (27, 28, 29).
  • Eat more protein: A high-protein diet increases fullness and reduces hunger. One of the mechanisms behind this is a reduction in ghrelin levels (30).
  • Maintain a stable weight: Drastic weight changes and yo-yo dieting disrupt key hormones, including ghrelin (31).
  • Cycle your calories: Periods of higher calorie intake can reduce hunger hormones and increase leptin. One study found 2 weeks on 29–45% more calories decreased ghrelin levels by 18% (32).
Bottom Line:

Maintaining a stable weight, avoiding long dieting periods, eating more protein and getting more sleep can help optimize ghrelin levels.

Take Home Message

Ghrelin is a very important hunger hormone.

It plays a major role in hunger, appetite and food intake. Because of this, it can have big effects on your success with weight loss and maintenance.

By having a sustainable and enjoyable diet plan, you can avoid the yo-yo dieting that causes large fluctuations in weight and negatively affects your hormones.