Anorexia nervosa (AN) is a serious eating disorder characterized by extreme restriction of food intake, leading to significantly low body weight. This severe state of malnutrition affects the gastrointestinal (GI) tract. While many people associate AN with constipation, the condition can also directly or indirectly cause diarrhea. Understanding the physiological changes and behavioral patterns associated with AN helps clarify why this symptom occurs.
Behavioral Causes of Gastrointestinal Distress
One of the most direct causes of diarrhea in individuals with AN is the misuse of laxatives. Laxative abuse is a compensatory behavior often employed in an attempt to prevent weight gain or relieve the sensation of fullness. Stimulant laxatives work by irritating the lining of the colon, forcing contractions and rapid expulsion of contents, resulting in severe, watery diarrhea and a loss of body water. Chronic use damages the nerves and muscles of the colon, creating a dependency that leads to alternating cycles of constipation and diarrhea.
How Malnutrition Changes Digestive Function
Beyond behavioral factors, chronic starvation profoundly alters the digestive system, making it prone to dysfunction. Prolonged lack of nutrients causes atrophy, or wasting away, of the intestinal lining, particularly the villi. This villous atrophy reduces the surface area available for nutrient absorption, and impairs the production of digestive enzymes, leading to malabsorption.
Undigested food components, such as fats and carbohydrates, remain in the intestine, creating an osmotic effect that pulls excess water into the colon. This increased water content and unabsorbed material results in osmotic diarrhea. Furthermore, the severely restricted diet seen in AN shifts the balance of the gut microbiome, and this reduced bacterial diversity can contribute to GI distress.
The Role of Refeeding in Diarrhea
Diarrhea is a common issue that arises during the initial phases of nutritional rehabilitation, or refeeding. This occurs as the body’s starved digestive system attempts to process a suddenly increased load of food. The rapid introduction of nutrients, especially carbohydrates and fats, can overwhelm the still-atrophied gut.
The intestinal lining struggles to break down and absorb the newly introduced food. This malabsorption effect causes osmotic diarrhea, as the large volume of undigested material draws water into the bowel. Enzyme deficiencies resulting from prior malnutrition further compound the issue by slowing the chemical breakdown of starches and fats. Clinicians manage this stage carefully, recognizing that this diarrhea is a temporary and expected side effect of recovery.
Managing Symptoms and Clinical Risks
Persistent diarrhea in a patient with AN presents serious clinical risks, most notably the loss of fluids and electrolytes. Dehydration can rapidly become severe, and the loss of minerals like potassium (hypokalemia) is particularly dangerous. Hypokalemia can cause muscle weakness, cramps, and, in severe cases, cardiac arrhythmias.
Treatment requires an integrated approach that focuses on addressing the underlying eating disorder and restoring nutritional status. Managing symptoms often involves temporary dietary adjustments, such as reducing the intake of high-fiber or high-fat foods, which are difficult for a compromised gut to digest. Anti-diarrheal medications are generally avoided in favor of allowing the body to heal with careful, supervised refeeding and hydration.