Anorexia nervosa damages nearly every organ system in the body. It carries the highest mortality rate of any mental illness, with people diagnosed with an eating disorder more than twice as likely to die from any cause compared to those without one. The damage ranges from reversible changes that improve with weight restoration to permanent harm that persists even after recovery. Here’s what happens inside the body when it’s chronically starved.
Heart and Cardiovascular System
The heart is one of the first organs affected and one of the most dangerous targets. The most common cardiovascular findings in anorexia are bradycardia (a resting heart rate below 60 beats per minute) and low blood pressure (below 90/60 mmHg). These sound like signs of fitness in an athlete, but in a malnourished body they reflect a heart that’s weakening and slowing down to conserve energy.
The heart is a muscle, and like every other muscle during starvation, it shrinks. Anorexia reduces the mass of the left ventricle, the chamber responsible for pumping blood to the rest of the body, which lowers overall cardiac output. In a study of 43 patients with anorexia, 37% had mitral valve prolapse, a condition where a heart valve doesn’t close properly. This happens because the heart muscle atrophies while the valve stays the same size, creating a mismatch.
The most life-threatening cardiovascular risk comes from electrical changes in the heart. Prolonged starvation and electrolyte imbalances can disrupt the heart’s rhythm, lengthening the interval between beats in ways that increase the risk of sudden cardiac death. One case report documented a patient whose first sign of anorexia was cardiac arrest, triggered by a potassium level of 1.8 mmol/L, dangerously below the normal range of 3.5 to 5.0. Standing up can also become risky: a spike in heart rate of more than 30 beats per minute when moving from lying to standing signals serious cardiovascular instability.
Bone Loss and Fracture Risk
Anorexia strips bone density at a pace most people don’t see until old age. Between 50% and 90% of people with anorexia develop osteopenia (thinning bones), and 20% to 30% progress to full osteoporosis. This happens through a combination of nutritional deficiency, low body weight, and hormonal disruption, particularly the drop in estrogen that accompanies starvation.
Unlike many other effects of anorexia, bone loss is one of the hardest to reverse. Even after weight restoration, bone density may never fully return to normal, especially if the illness occurred during adolescence when bones are still building toward their peak strength. This leaves people with a lifelong increased risk of fractures.
Hormones and Reproductive Health
Starvation throws the body’s hormonal control center into crisis mode. The brain essentially shuts down the reproductive system, cutting the signals that trigger ovulation in women and reducing testosterone in men. This is why loss of menstrual periods is one of the hallmark signs of anorexia in women. It’s not just a surface symptom. It reflects a deep suppression of estrogen and other sex hormones that affects bone health, mood, and long-term fertility.
At the same time, the body’s stress hormone system goes into overdrive. Up to 80% of women with anorexia have elevated cortisol levels, the hormone normally released during acute stress. Chronically high cortisol breaks down muscle, weakens bones, impairs immune function, and further suppresses the reproductive system. Adolescent boys with anorexia show lower testosterone, lower estradiol, and reduced lean mass compared to healthy peers.
Brain Shrinkage and Cognitive Effects
Brain atrophy in anorexia is one of the most dramatic structural brain changes seen in any mental illness. Imaging studies show that people with anorexia have reduced gray matter volume, particularly in the frontal lobes and the insula. Gray matter is the tissue responsible for processing information, making decisions, and regulating emotions.
The frontal lobes govern executive functions like planning, attention, working memory, and self-control. Losing volume there translates into real cognitive difficulties: trouble concentrating, impaired decision-making, and rigid thinking patterns that can make recovery harder. The insula plays a role in how you perceive your own body, including hunger signals and body image. Reduced volume in this area may contribute to the distorted body perception that characterizes anorexia. The brain also loses volume by gaining cerebrospinal fluid in the spaces where tissue has shrunk. Some of this gray matter loss can improve with sustained weight restoration, though the timeline and completeness of recovery varies.
Blood Cells and Immune Function
The bone marrow, where blood cells are produced, deteriorates during prolonged starvation. In severe cases, the marrow atrophies and is partially replaced by a gelatinous substance and fat, reducing its ability to produce the three main types of blood cells. The consequences show up in blood work: anemia occurs in 21% to 39% of patients, low white blood cell counts in 29% to 39%, and low platelet counts in 5% to 11%.
Low white blood cell counts are particularly dangerous because they weaken the immune system. Research shows that patients with lower BMI or more severe drops in white blood cells face a higher risk of serious infections. This is one reason people with severe anorexia can become critically ill from infections that a healthy immune system would fight off easily. These blood cell changes are generally tied to the degree and duration of malnutrition and tend to improve with nutritional rehabilitation.
Digestive System Damage
The gastrointestinal tract slows down significantly during starvation. Delayed gastric emptying, where food sits in the stomach much longer than normal, is common in restrictive anorexia. The smooth muscles lining the intestinal tract atrophy, leading to sluggish movement of food through the entire digestive system. This creates a painful cycle: the person feels uncomfortably full after eating even small amounts, which reinforces the avoidance of food.
Intestinal transit slows as well, often causing severe constipation and bloating. These symptoms can persist into early recovery, since the digestive system needs time to regain its normal motility and capacity. During refeeding, meals are typically reintroduced gradually to avoid overwhelming a gut that has adapted to processing very little.
Skin, Hair, and Temperature
Visible changes to the skin and hair are often among the first signs other people notice. Hair thins and falls out as the body diverts limited nutrients away from non-essential functions. At the same time, fine, downy hair called lanugo may appear on the face, arms, and torso. This isn’t random. The body detects that it can no longer regulate its own temperature and triggers the growth of this insulating fuzz through the same molecular pathways that produce it in fetuses before birth. Skin becomes dry and may take on a yellowish tint from changes in how the body processes certain nutrients.
Electrolyte Emergencies
Electrolytes like potassium, sodium, and chloride keep the heart beating, muscles contracting, and nerves firing. Anorexia depletes these minerals through inadequate intake, and purging behaviors (if present) accelerate the losses dramatically. Potassium is the most dangerous to lose. Normal blood potassium runs between 3.5 and 5.0 mmol/L. Levels below 2.5 can cause dangerous heart rhythms, and levels around 1.8, as documented in at least one case of cardiac arrest, can be fatal without immediate intervention.
These imbalances can develop quickly and without obvious warning signs. A person might feel muscle weakness, tingling, or an irregular heartbeat, but sometimes the first indication is a medical emergency. Electrolyte monitoring is one of the most critical aspects of medical care during both active illness and the early stages of refeeding.
Mortality Risk Over Time
A large primary care cohort study found that people with an eating disorder diagnosis were five times more likely to die from an unnatural cause within the first year of diagnosis and 5.4 times more likely in years one through five. The risk of death by suicide was 14 times higher in the first 12 months after diagnosis. Even beyond five years, the risk remained nearly three times higher than the general population. At the 10-year mark, there were 341 excess unnatural deaths per 100,000 people with an eating disorder diagnosis compared to those without one. The physical damage to the cardiovascular system, kidneys, and electrolyte balance accounts for a significant share of these deaths, alongside the psychiatric toll of the illness itself.