Anorexia Nervosa (AN) is a serious eating disorder characterized by restriction of energy intake, a fear of gaining weight, and a distorted body image. The severe malnutrition initiates a cascade of physical complications, including gastrointestinal problems like bloating, abdominal pain, and chronic constipation. This slowdown of the digestive system is a direct physiological consequence of starvation, reflecting the body’s efforts to conserve energy. Understanding the mechanisms behind this symptom is fundamental for managing the condition during treatment and recovery.
The Physiological Slowdown
When the body is subjected to prolonged undernutrition, it adapts by drastically lowering its overall metabolic rate to conserve energy stores. This systemic slowdown includes the digestive tract, impairing the muscles responsible for moving food and waste. Reduced energy availability leads to decreased peristalsis, the wave-like muscular contraction that propels material through the intestines.
The nervous system also suppresses parasympathetic activity, often called the “rest and digest” system, in favor of energy conservation. This change contributes to gastroparesis, or delayed stomach emptying. The slowed transit time means waste material sits longer in the colon, allowing excess water to be reabsorbed and leading to hard, dry stools.
Hormonal changes further contribute to this digestive impairment, particularly the suppression of the thyroid axis. Low levels of thyroid hormones are a common adaptation to starvation and directly influence the speed of gut motility. This combination of reduced muscle strength, altered nervous system control, and hormonal changes creates an environment where the entire gastrointestinal tract operates in a state of hypofunction.
The Impact of Reduced Dietary Bulk
Beyond the metabolic slowdown, the physical lack of material in the digestive tract is a major mechanical cause of constipation. Stool requires adequate mass and volume (bulk) to properly stimulate the nerves and muscles that trigger a bowel movement. When caloric intake is severely restricted, insufficient waste material is generated to initiate the defecation reflex.
Fiber adds necessary bulk to the stool, helping it retain water and move smoothly through the colon. Diets low in food volume are often deficient in fiber, removing this natural laxative effect. Dehydration is also common, as individuals may restrict fluid intake out of fear of bloating. This lack of water causes the minimal waste material to become excessively hard and difficult to pass, worsening constipation.
Navigating Constipation During Recovery
Constipation remains a significant challenge during the initial phases of nutritional rehabilitation and weight restoration. As refeeding begins, the digestive system processes a greater volume of food, which can initially worsen symptoms like bloating and discomfort. Medical supervision is necessary to manage the reintroduction of calories safely and monitor for potentially dangerous electrolyte imbalances.
A particular complication is the history of laxative misuse, which can cause long-term damage and dependence, making the restoration of natural bowel function difficult. For safe management, healthcare providers typically recommend interventions like osmotic laxatives and stool softeners, such as polyethylene glycol, which draw water into the colon.
Stimulant laxatives are generally avoided due to their potential for abuse and their tendency to exacerbate long-term gut dysfunction. The most effective and long-term solution for resolving constipation is nutritional rehabilitation and weight normalization.
As the body recovers from malnutrition, gut motility typically improves, often normalizing within four to twelve weeks of consistent refeeding. Restoring a consistent pattern of eating, alongside a balanced, fiber-appropriate diet and adequate hydration, is the most reliable way to signal that normal physiological functions can resume.