What it means
Ghrelin levels tend to climb before usual mealtimes and fall after eating. It acts on appetite centers in the brain and also affects growth hormone release, fat storage and blood sugar.
After diet-based weight loss, ghrelin levels often rise. Many researchers see this as part of the body's push to regain lost weight, along with lower leptin and a drop in calorie burn.
The "hunger hormone" label is a simplification. Studies in animals and people show that appetite depends on many signals working together, including GLP-1, PYY, insulin, leptin, sleep, stress and food cues, and ghrelin alone does not explain hunger.
Poor sleep has been linked to higher ghrelin and more hunger in some studies. Protein and fiber at meals may help keep hunger steadier for some people, though individual responses vary.
Why it matters
Rising ghrelin after weight loss helps explain why hunger can come back when GLP-1 treatment stops.