Ghrelin is a signaling hormone produced predominantly by the stomach that regulates energy balance and appetite. It is often known as the “hunger hormone” because its primary action is stimulating food intake. While much focus is placed on its involvement in obesity, a deficiency in ghrelin can lead to distinct health concerns. This condition arises when the body produces pathologically insufficient levels of the substance. Understanding low ghrelin levels requires examining its normal function, causes, and resulting systemic consequences.
The Normal Function of Ghrelin
Ghrelin is the only known gut-derived hormone with an appetite-stimulating (orexigenic) effect. Its main purpose is to signal the hypothalamus in the brain that the stomach is empty and that it is time to eat. The body releases ghrelin cyclically, with levels rising sharply before a meal and quickly decreasing after consumption. This fluctuation suggests its role in the short-term, meal-to-meal regulation of food intake.
Beyond regulating hunger, ghrelin performs several other functions related to maintaining energy stores. It stimulates the pituitary gland to release growth hormone, which helps regulate body composition by promoting muscle building and fat breakdown. The hormone also influences gastric motility, helping food move through the digestive tract. Furthermore, ghrelin affects glucose metabolism by influencing insulin release and promoting the use of carbohydrates as a fuel source.
Medical Conditions That Cause Low Ghrelin
A significant reduction in circulating ghrelin most commonly occurs as a direct result of surgical intervention. Bariatric procedures, particularly sleeve gastrectomy and Roux-en-Y gastric bypass, often lead to a sustained decrease in ghrelin levels. This occurs because the fundus, the upper part of the stomach, is the primary production site for ghrelin, and a large portion is either removed or bypassed during these operations. The resulting hormonal change contributes to the post-surgical reduction in appetite and subsequent weight loss.
Other health issues can also be associated with pathologically reduced ghrelin levels. These include gastrointestinal disorders that affect the stomach lining, such as chronic gastritis or H. pylori infection. Conditions like functional dyspepsia and short bowel syndrome have also been observed to involve lower ghrelin concentrations. Low levels are sometimes observed in individuals with obesity, though this relationship is complex.
Physiological Consequences of Ghrelin Deficiency
The most direct consequence of ghrelin deficiency is a profound reduction in appetite, known as anorexia. Without the strong hunger signal, individuals may experience a lack of desire to eat, even after long periods without food. This decreased food intake often leads to significant, involuntary weight loss and potential malnutrition, as the body struggles to maintain an adequate caloric balance.
The deficiency also impacts metabolic processes, particularly glucose homeostasis. Ghrelin normally suppresses insulin secretion, so its absence can alter the body’s management of blood sugar. Furthermore, the lack of ghrelin stimulation on the pituitary gland may impair growth hormone release. This indirectly affects body composition by altering the balance of fat accumulation versus lean muscle maintenance, and in younger individuals, it could impact normal growth.
Ghrelin also plays a role in gastrointestinal motility, and its deficiency can be associated with delayed gastric emptying. This slowed transit time can lead to feelings of premature fullness, nausea, and bloating. Some research suggests a link between low ghrelin levels and changes in mood, including reduced motivation and an increased risk of depression.
Identifying and Treating Ghrelin Deficiency
Diagnosis of ghrelin deficiency typically begins with a clinical evaluation of symptoms, such as persistent appetite loss and unexplained weight loss. Confirmation requires specific blood tests to measure the circulating levels of the hormone. These tests often measure both the active, acylated form of ghrelin and the total ghrelin concentration. Comparing these results to established reference ranges or to levels of other appetite-regulating hormones, like leptin, helps confirm the diagnosis.
Management strategies focus on addressing the underlying cause and managing the resulting symptoms. If the deficiency is an intended outcome of bariatric surgery, treatment focuses on nutritional support and monitoring to ensure adequate caloric intake. For patients with chronic diseases causing low levels, the primary focus is treating the underlying condition. In instances of severe appetite loss, therapeutic avenues may involve the use of appetite stimulants. Current treatment remains largely supportive and individualized, though research continues into the potential for ghrelin replacement therapy.